Well, you will want to explore the cave which the yeti was in -- it's only one screen but it has a missable item that you need to beat the game.
EDIT: Unsure whether the obtuse inventory puzzle in the forest is worse than the many, many missable needed-to-win items (as in, no way to backtrack to get them). Their use isn't even generally obvious until it's too late to get them.
There aren't too many missable items in KQ6, thankfully, due to the less linear nature of the game. There are still a couple things here and there you might not do but they only count for points, and won't lose the game for you. Generally the game gives you very good advanced knowledge of when you're missing items -- in the easiest place to make the game unwinnable (Catacombs) they actually tell you that you're not ready (the first time) if you don't have all the items, but if you do they just throw you in straight away (if you know this you can figure out without too much trouble what you actually need).
Most other cases if you've missed an item it's because you actually screwed up. It's also generally possible to still win the game without them -- there are a couple dickish ones near the end, though.
Compare that to KQV's forest, in which the game just kills you if you've gone in without the items you've needed, not preventing you from entering, and never giving you any idea of what items you actually need.
Mordack has now been defeated! I'd say more if I wasn't so put off by how ridiculous the ending was. It amuses me that everything in this game is resolved with a literal Deus Ex Machina and a liberal dosage of Chekov's gun.
On a semi-interesting note, since I've finished the game I've been reading up on version differences. Apparently in at least the NES and floppy disk versions, the wand you get actually has a use -- you have to use certain spells throughout the game. Supposedly what these spells all do involves cyphered prompts that you need the guidebook that the game came with to decode, so it serves as a basic copyright protection.
The cypher key is still in King's Quest Collection, but it serves no use; the CD-ROM version completely lacks that. (Frustratingly, as others have noted, the CD-ROM version also doesn't include a subtitled/text version of the game, the way the floppy version was. The sequel thankfully didn't have this issue.)
Interesting, I always wondered about that. I knew my way through the game pretty well as a kid, and I remember a friend of mine calling me for help. Apparently he found the bandit's hideout, but it wouldn't let him enter the tent because the game was telling him to cast a spell with Krispin's wand to put the bandit asleep. Of course, I had the CD-ROM version and had no idea what he was talking about.
I do remember King's Quest VI pulled some bullshit like that as well. You have to solve a series of puzzles to get to the top of a cliff, but doing so requires looking up the hints to the puzzles in the instruction manual. To make matters worse, every walk-through I was able to find at the time refused to give the answers for "copyright reasons." It really screwed me over since I was playing a second-hand copy that didn't come with a guide.
Last night was when the game truly PO'ed me. Thpoilerth:
So there's this boat that Graham comes across, and worthless-as-ever Cedric is really eager for Graham to get into it. Well, I take it out to shore and then he tells me there's a hole in the boat and it sinks. Well, why the frick didn't he mention that to start?! And if you look at the boat, no mention is made of the hole! The game gives you no advance warning; you have to die at least once unless you've looked up an FAQ in advance. Of course, the solution is easy (plug the beeswax into the hole), but... I don't get it. Either the developers thought this was too easy and put this artificial imposition on it, or this was just a case of poor playtesting. Whatever the case, it is INEXCUSABLE.
There's been harder puzzles and deaths to figure out in the game up to now, but it took this one to honestly offend me. I WILL continue on with the rest, though it will be a grudging trudge to the finish.
I gave up on the NES version. It discarded my save when I turned it off and I'm not going to write down those damn passwords. Luckily, I managed to find my old KQ5 CD-ROM, so I'll just start over on that.
Also, if anyone is feeling REALLY masochistic, try out Kings Quest 3. I hope everybody involved with the development of that game dies a slow horrible death... okay not really. But it's still extremely difficult, even if you have a guide.
Welp, I've beaten it. Honestly, it was a fun experience, if not just because it was sadistically fun to see everyone else suffering. ;D
Ah, but the game really was a product of its time, so I can't be TOO hard on it. However, I'm now playing KQ6, and it's a CONSIDERABLE improvement over its predecessor. I'll try to beat it within a week also and research whatever other adventure games I can on the side. I assure you this podcast is going to be big, so don't miss out!
I finished the game today, which was only possible because of all the help I got last night in the IRC channel.
The game was charming at first. Rather than criticize it, I'll just say that I don't think we (i.e., people of the distant year 2012) can consider ourselves the intended audience here. KQV's audience was our 1990 equivalents, who were delighted by the little dancing man in their Packard Bell and all the ways he managed to die.
So if your goal was to impress people and reward their curiosity, the game is pretty good. The puzzles can't be logical, or you'd solve them too quickly and miss out on all the funny stuff. And there's a lot of cool and funny stuff to try and see.
But even by these standards, the game starts to feel tired about halfway through. You use the same magic harp to escape two very similar predicaments. You help one doomed animal after another, and are repaid for your kindness in increasingly cliche ways. Perhaps most disappointing of all, after placating the ice witch lady, the game is pretty much just a straight line to the finale. Rather than wandering around a new environment, looking at strange new places and wondering how to get inside, you're just whisked away to place after place without warning.
Anyway, here's my favorite screen from the entire game, occurring toward the end.