Okay, what are people's most difficult individual puzzles in any Myst game?
My own personal 'most difficult list':
Any involving recognising musical notes or sounds. I am tone deaf (in the proper sense) and have no chance whatsoever with these puzzles such as the spaceship organ in Myst, the Mangrees in Revelation, the 'whirrs and pings' on Catherein's prison in Riven.
Also very difficult: Most of Spire (what the?), the Stone circle in Riven (i worked out the numbers and animals completely right but still couldn't get the order right thanks to the ultra-abstact nature of the animal drawings), the elevator in Exile (again, we had to work from 'diagrams' that were not remotely clear)chinaboatman@hotmail.com

I think the default answer to this question is "The fire marble puzzle in Riven." But even though I needed a bump from the hints for that one, I'd already come very close to solving it on my own, and enjoyed the challenge.

What was more frustrating were the tasks in Myst IV. I finally just got frustrated and quit Revelation without finishing. Even with walkthroughs, there were some areas I couldn't finish. I like a game where I can solve the majority of puzzles unassisted, and Myst IV was like that at first, but I eventually hit the wall. Deductive puzzles where you take note of elements in the environment, then apply them to a solution, are my favorites. When they get a bit more esoteric, or depend on dexterity with the mouse, my opinion tends to be mixed. If they're still logical, sweet! But if they take a task that would be easy in real life and make it near impossible thanks to the interface, I'm not interested.

Mowog

Mowog, I'll bet you hit the wall in Dream. If you give it another try you could be surprised at how it "comes to you" after fooling with the puzzles for a time. They don't yield to "logic" very well, but there's a certain pattern that you can discern after a while. It's a shame you didn't finish the game as it has a nifty ending, as you no doubt know.

I agree about the 'environment puzzles'. Working out what goes where and how everything fits together is my favourite aspect too. Probably why i liked Riven so much.
I actually found 'Dream' and indeed the whole of Serenia very easy. I pretty much did it in one (v long)sitting. As always, the 'dilemma' at the end was a no-brainer.Agree, it was a good ending. Good story generally. Probably the best game in the series along with Riven. It was Spire which baffled me! But Revelation was more difficult than usual, i agree.

Difficult individual puzzles in Myst games...well, let's see:

Myst - Not a difficult game. I've found some problem in gettin through the maze,though.I've found that part too long and boring.

Riven -The stone circle puzzle and the devilish fire marble puzzle: this one had clues scattered all over the place!

Exile - The whole age of Amateria was challenging enough.

Revelation -The spider chair, no doubt: I've lost my sleep on that puzzle!!

Uru -(sorry Chinaboatman, but I DO consider Uru as a Myst game) Kadish Tolesa's final puzzle, the one that granted access to the Bahro's cave.

End of Ages -Too easy.I've had some minor problem in Noloben, first in accessing Esher's lab,and then having the Bahro to open the Keep's door for me.

So, in the end, wich one win the first prize?
The winner is...Riven, the fire marble puzzle!!
In my opinion, of course!

Riven was probabaly the game that took me longest to complete but that was mainly because i was stuck forever on the stone circle. It was easy to work out what to do, it was just doing it! I knew the frog and its number for example but couldn't work out which picture was supposed to be the frog! I've since seen the walkthroughs of course and we were supposed to be able to work it out from the shapes in rocks and water and stuff. I cannot comprehend anyone getting them all!

I'm taking a long time to get through Myst V, not because it's difficult but because i have trouble motivating myself to actually play it! But i've covered my dislike of it pretty thouragly by now...

No other puzzle/problem even comes close to being as difficult as the dreaded spider-chair in Myst IV! I still don't know where the clues are found that enable you to be able to figure-out it's solution.

Riven, Uru, Until Uru, and Myst IV are my favorites of the series, not necessarily in that order.

The hardest puzzle for me is the Spider Chair in Revelation. My computer simply couldn't process the game fast enough for me to complete it. I don't think that type of puzzle fits into the Myst series anyway.