There is a post that could be developed here, in this forum:
"Chatting with a game designer friend the other day and we were bemoaning the state of adventure game puzzles and it got us talking. So I was wondering what is your favorite puzzle in Thimbleweed Park, Maniac Mansion, Monkey Island or any other classic point-and-click game?
Do you like head scratchers? What makes a puzzle good? What makes a puzzle hard? What makes a puzzle just busy work? Is that bad?"
– Ron Gilbert
I’ll just get it out of the way: The Monkey Wrench Puzzle™
I’ve read @RonGilbert’s blog post and I’m astonished that you guys actually have favorite puzzles. I really can’t say which of the puzzles are my favorites.
The puzzles I remember are mostly unique ones (like the sword fight insults) or puzzles that are playing with expectations (like the cannibals in MI). But I really can’t say which of them are my favorites. Maybe because they are always embedded in a puzzle chain. For example …
… is actually a puzzle chain and/or linked with other puzzles.
The Broom Alien puzzle stands out to me.
I like the feeling when there’s a character or item that was puzzling you for a long time, and then you finally see it’s purpose in the game.
I love puzzles where you have non-obvious, yet perfectly logical solutions. Or ones where you find a new way of using an object you already used.
I can’t think of any example now. I’m too tired.
Chekhov’s Broom!
I generally like puzzles where you have to complete a recipe with substitutes or unconventional ingredients. Both MI1 and MI2 had some of those, I think. Makes you feel clever and the result is often quite funny (if gross).
As for puzzles that stand out particularly, two come to mind:
In Deponia 2, where you had to turn off the background music. Wonderfully out of the box thinking and 4th wall breaking in one 
.
And Deponia 4, the puzzle with the jackalopes machine. Not so much for the puzzle itself, but how cleverly it was tied into the overall story. It’s basically the catalyst that sets all the events in motion, and that came quite unexpected. Probably hard to pull off unless a game has time travel or some sort of flashbacks.
My fav has to be the one from Zak where you need to distract the flight attendant by doing bad stuff.
I don’t like that one for two reasons: the first one is that I used to play without music because I needed to hear if my daughter woke up, so I completely missed it. The second one is that it’s not a good puzzle. It breaks the contract between player and game, there’s nothing in the game that suggests you may need to use “real world” stuff to solve it. If it were a puzzle game and not an adventure game, that would have been OK, but that one is just plain unfair.
Which is why I find it remarkable. Sure, it’s nothing you’d want to see in a serious game (or a game that takes itself seriously), but Deponia is already full of transgressions, what’s one more!?
Besides, everything still takes place within the confines of the game, and the hints provided weren’t that bad, I think.
Bold statement in a Thimbleweed Park Forum 
I liked that one very much.
I particularly liked what Sam & Max Season 3’s episode “The Tomb of Sammun-Mak” did with those film reels. Those are some sort of flashbacks, but interactive and affecting each other. Very clever and indeed similar to some time travel stories.