I've come to the conclusion that it's not the logic behind the puzzle solution that matters; rather, it's how you present the puzzle to the player. A puzzle only works well if the player thinks the same way the developer does—and just like any platformer or FPS or RPG, there needs to be a learning curve to ensure the player is thinking the way the developer wants him or her to. A great idea for a puzzle is only the beginning—the implementation is critical.
Based on my experience as a player, along with my experience as a Dungeon Master who likes to throw riddles and puzzles at his Dungeons & Dragons players from time to time, here are three key rules I've developed for implementing puzzles that are both intuitive and enjoyable:
1.) Make it clear that there is a puzzle. There's a big difference between exploration and aimless wandering—keeping the players focused on accomplishing tasks and overcoming obstacles strengthens the story and makes the gameplay more engaging than if the players spend the whole game looking for something to do.
2.) Provide clear and consistent feedback about what does and doesn't work. Adventure game players are problem-solvers, not mind-readers; unclear, misleading, and absent feedback about a player's actions can ruin even the most logical puzzles.
3.) Establish clear causality. People of all different cultures, languages, religions, and educational backgrounds will potentially play your game—the more your puzzle solutions rely on knowledge not communicated inside the game, the more likely your logic will come across as baffling and obtuse to anyone who doesn't share your background or way of thinking.
To help emphasize the importance of these three rules, I'd like to present a series of examples from King's Quest V—which prompted this post in the first place—that demonstrate how a conceptually sound idea can provide a great challenge in one game but a terrible challenge in another, depending on the implementation. Needless to say, spoilers ahoy.
Challenge: Enlist the help of others to accomplish something you can't do alone.
A recurring theme in King's Quest V is helping others who, in return, help you. After tricking a meddlesome dog into leaving the colony of ants it's been terrorizing, the leader of the ants (whose speech you can understand due to some magic) thanks you profusely and offers to help you in any way you might need. Now, one might expect to be able to talk to the ants again to request a favor, or perhaps to see an ant icon on the inventory screen that can be used to call in the ants precisely where you choose. Instead, you get...nothing. The ants don't discuss the offer further, so you can only assume you'll need to come back and ask again once you've come across something they can help with.
Wrong! All you have to do is click on the right object, and the ants will automatically deploy. Perhaps you've seen the haystack behind the inn. Perhaps you searched it, hoping to find the proverbial needle, with no success. Perhaps you noticed the back door of the inn, which is near to the haystack, and began envisioning a scenario where you could get the bandits inside the inn to chase you through the back door, at which point you could dive into the haystack and wait for the bandits to disperse in search of you elsewhere, leaving the inn empty for you to safely explore. Perhaps you weren't expecting anything different to happen when, out of tired desperation to figure out what to do next, you clicked on the haystack for a second or third time. Perhaps you were surprised to see a colony of ants march into the haystack without any prompting whatsoever, coming from a screen that isn't even within earshot of this one, to retrieve an item (the proverbial needle) that you haven't been given a reason to search for, especially after the game told you the first time you clicked that there were no needles in this haystack! All three rules are thrown to the wind here.
It should also be noted that Cedric, the owl who follows you throughout the entire game, does not once offer to lift a finger (assuming owls have fingers) when it comes to doing anything he could possibly help with. Cedric, could you hop onto those icy platforms to see if they break under your weight before I go hopping on them? Cedric, could you distract the gypsy man so I can sneak into his wagon? Cedric, could you swoop in and pluck that poisonous snake from the path while his attention's on me? No? Of course, Cedric. Tell me how to get to the bakehouse again, because that's all you know how to do.
Gemini Rue is a game that does this kind of challenge right. There's a tense sequence relatively early in the game where you and your buddy Matthius are trying to escape from a building that's now swarming with enemy goons. You make a break for the exit, but you can't get the door to the roof open. Trapped at the end of the hallway, you have only moments to open that door before bad guys start pouring in through the way you entered. Fortunately, you're not alone—Matthius is just as capable of kicking doors and picking locks as you are, and you can instruct him to perform different actions on anything you can click on. With a little teamwork, you can make it out alive. All three rules are intact here: it's obvious that the door to the roof is the only way out; you get clear and immediate feedback from the game about how Matthias can be used to assist you; and the consequences of your actions (and inaction) are plainly visible and stem from the logical interplay of armed goons, two average-strength heroes, one door you can open, and one door you can't.
Challenge: Navigate an area that's seemingly endless.
In King's Quest V, the land of Serenia turns into endless desert if you travel far enough west. Cedric the talking owl tells you that. And even if you didn't believe him, you'd find out for yourself, and end up dying of dehydration after a few screens. It truly is nothing but desert. You start to make a map, or perhaps move systematically through the desert, but then you notice the same four screens repeating. And then you die of dehydration again. Heck, the northernmost part of the desert is up against a steep cliff, and that's the same screen over and over if you try to cross the desert up there. Besides, you've played King's Quest III and you remember that there's nothing across any given endless desert except death. You have absolutely no reason to explore the desert. You've ventured into the desert three times, in three different places, and there is nothing there.
Except for the oasis you missed that's four screens in. And the skeleton with the grody old boot. And the bandit tent with the magic staff that lets you into the temple with the coin and the bottle you need in order to solve two of the game's most pivotal puzzles. But you've already explored about 20 screens of the explicitly-stated-to-be-endless desert and found nothing but dehydration, death, and reused backgrounds. So, no, as far as you're concerned, there is nothing out there. If you happen across a jug of water or somesuch later on, perhaps you'll bother with the desert again. Until then, out of sight, out of mind.
You never do find that jug of water.
In The Secret of Monkey Island, there's an underground network of lava-filled caves that is so confusing to navigate that the landscape might completely change when you backtrack to a screen you were just on. You know for a fact that you'll have to go through here to reach the villainous Ghost Pirate LeChuck, but even if you hadn't just spent this entire portion of the game trying to gain access to this area, this confusing maze is too far out of the way to simply be a dead-end. Based on your experience with the confusing forest earlier in the game, there's gotta be some trick to getting through...and so there is: some cannibals who captured you earlier mentioned a Head of the Navigator that'll be perfect for the job.
King's Quest V violates Rule # 1 and Rule # 2 with its endless desert--there's no obvious need to enter the desert, and the feedback you get about the desert all points to it being a dead-end that's meant only to kill you, or else a place you're not ready to enter yet. The Secret of Monkey Island, on the other hand, leads you directly into the endless caves, so there's no question of whether you should bother with them, and makes a puzzle out of obtaining the item you know you need to make it through the caves—though you're certainly welcome to try navigating them on your own.
Challenge: Avoid detection.
By the end of King's Quest V, you've infiltrated the castle of the evil wizard Mordack in an attempt to rescue your family. As far as you can tell, Mordack is unaware of your presence, so you poke around the castle a bit, taking your time to examine your surroundings. Halfway across the dining room, Mordack appears out of nowhere and magically chokes you to death, offering you no opportunity to defend yourself or run away. Okay, you think to yourself as you reload, maybe walking around out in the open is a mistake. I'll stick to the walls and move faster next time. On your second attempt, you get a little deeper into the castle, but Mordack still shows up and puts an end to you. Wow, you think. There really isn't any time to lollygag. I'll rush through next time and will examine each room more closely once I've got a way to protect myself. Yet even that doesn't work; it seems there are specific locations where Mordack will show up no matter how quickly you move, but his timing elsewhere is still unpredictable—sometimes he shows up right away, and sometimes he lets you go through several rooms without incident.
King's Quest V fudges Rule # 1 and ignores Rule # 3 altogether. What, exactly, is the puzzle here? Is it avoid Mordack? Is it confront Mordack? Is there a pattern to his movements? Is there something specific you're doing (or not doing) to hasten his arrival? Is this just a sign that you shouldn't be poking around the castle until you've done something else first? Who knows?! If you're going off of your encounter with the witch back in the forest earlier in the game, then the obvious answer is that Mordack appears at random and you need a powerful magical charm to ward off his attacks...but the real answer is that you first need to thwart one of his goons—a big, blue beast that appears at random and for some reason hasn't shown up for you yet—so that Mordack will appear less frequently. The nature of the puzzle is unclear, the relationship between the different components is unclear, and there's a randomized, unrelated component you don't even know you're missing!
Contrast this with Space Quest I, which starts you off aboard a starship that's been invaded by hostile aliens. Every so often, you'll see a message that you hear footsteps; moments later, alien soldiers show up. It becomes apparent after the first encounter that they shoot on sight, so unless you can rustle up a weapon of some sort, the only way to survive is to avoid them. Outrunning them is difficult, if not impossible, but there are elevators you can duck into to hide from them—and the game congratulates you the first time you evade the aliens. All three rules are fully intact here: You know enemy soldiers are actively patrolling the corridors, you're given a warning to go hide yourself, and you get clear feedback about whether your course of action is successful.
Challenge: Wait for the situation to change.
If you can stay alive long enough in King's Quest V to explore the top floor of Mordack's castle, you'll come across a strange machine with a plate on either side and large cones pointing down at the plates. After some experimentation, you discover that it's possible to activate the machine (nevermind how; dropping a piece of moldy cheese into the machine deserves a paragraph of its own). You also find that you can leave your useless magic wand on one of the plates, so perhaps you can drop something on the other plate to recharge your wand or something. Exploring the castle more, you find Mordack's bedroom and an adjacent library. There's a spellbook there, and you memorize the first two pages you see...but now what? Getting the machine to work seems like the only way you can recharge your wand to cast those spells and rescue your miniaturized family from their prison, but none of the items you have on you will do the trick. Are you missing something?
Yes. Obviously, you need to steal Mordack's wand.
But...it's never explicitly stated that you need Mordack's wand to complete the circuit on the machine, and the game doesn't let you figure that out for yourself by putting incorrect items—even magical ones—in its place. I tried transferring magic power into my useless wand from my no-longer-helpful magical amulet (nice job you did protecting me from Mordack's death magic!) but was denied without explanation. You figure there's gotta be something to put on the other plate, but there's not enough direction as to what that might be. Heck, you can't even tell that Mordack has a wand unless you're looking extremely closely; there's no grand flourish where his whips his wand around, so it usually looks like he just Force Chokes you to death. There's not even an indication that he's got a special place to store his wand—clicking on the little table where he eventually rests his wand gives you the same message as clicking on his bed. Rule #1 is on the rocks here, and Rule #2 is on vacation.
Even if you haven't figured out what the deal with the machine is, maybe you've considered secretly swapping out Mordack's wand for your useless one, so that he'll blindly pick it up and have it fizzle when he tries to kill you again. The problem is the same in either case: How do you get Mordack's wand? Every time Mordack appears, you die before you have any opportunity to react. You've played King's Quest III, and Mordack is the brother of the evil wizard from that game, so maybe Mordack also keeps his wand locked away in a safe when he's not choking you with it. Not seeing a safe anywhere, you scour each room from top to bottom, clicking on every object with every icon you have.
The solution? Wait in the library until Mordack appears in the bedroom to take a nap, at which point you can steal his wand and use it with the machine. OK, so let's throw all three rules into the bonfire now.
Standing around everywhere else in the castle has gotten you killed repeatedly, so there's no reason to think the library will treat you any differently--especially with a creepy eye over the doorway tracking your every move, like a magical security camera. At no point do you see any indication that Mordack is getting tired, or that his bedtime is approaching, or that there's anything he's got on his agenda today aside from killing you. And there's virtually no chance of accidentally discovering that Mordack takes a nap, because even the most thorough adventurer will run out of things to click on well before Mordack shows up: despite a grand variety of books and interesting objects on the table, you get one response for clicking anything on the bookshelf, and one response for clicking anything on the table that isn't the aforementioned spellbook. With as quickly as you've needed to move through the rest of the castle, it's unreasonable to expect the player to slow down so much when there's no obvious need or incentive to do so.
This wasn't a problem two installments ago—or, at least, it isn't a problem in King's Quest III Redux, a fan-made remake of the third game in the series. Mordack's evil brother Manannan is constantly on your case for a large portion of the game, but you've got a timer at the top of the screen that changes colors depending on how close Manannan is to checking in on you. Even without the timer, it's established almost immediately that Manannan goes about his evil business and has different things he likes to do in different rooms of the house. He'll bust you if you're in the wrong place at the wrong time, but he's clearly on a schedule, and he's clearly got more things to occupy his time than just turning you into a pile of ashes. Manannan's house is where he lives; it's not simply where you die. It wouldn't be unreasonable to expect a player to try waiting around in a specific location with that kind of foundation in place.
King's Quest V is chock-full of problematic puzzles; I'm only scratching the surface here. The rules of clear objective, clear feedback, and clear causality are broken left and right throughout the game. In my tirade about King's Quest IV, I reiterated that these games really aren't my style, but I'm wondering more and more as I play through the King's Quest series whether it really is just a matter of taste. If I can appreciate good game design in genres I'm not too keen on (such as tactical RPGs—I disliked playing Shining Force but I don't think it's a bad game), then I should be able to appreciate good game design in genres I love, regardless of my style preferences. I laud King's Quest V for its beautiful graphics, clean interface, decent story, and acceptable voice acting (even the high-pitched Cedric isn't that bad after playing through Mega Man X7); it's the gameplay that spoils it for me. I knew there would be aimless wandering, random events, and unannounced time-based challenges, but accurate expectations didn't make the game any more intuitive or enjoyable.
King's Quest VI, it's up to you to persuade me that your series can deliver both great ideas and great execution. I'll buy you a little time to prepare yourself--Quest for Glory has been calling my name, I'm due for another round of Leisure Suit Larry, and I've had this sudden hankering to play Tomb Raider 2. Be ready.