I honestly can't remember if I have actually play this game to its ending. Some of the puzzles are quite weird. But I do enjoy watching the making of video included as a a bonus here.
I (finally) finished it two years ago or so. I already tried it over a decade ago or more, but it was the microscope puzzle game that turned out to be too hard for me back then, the game that plays a bit like checkers, but in reverse.
Anyway, now I was somehow able to finally win that game. I don't recall if there were other equally hard puzzles, most were pretty easy and straightforward IIRC.
Then again, I don't quite consider the game a strong classic, it is merely a collection of unrelated puzzles with full motion videos in between with some strange over-acting. It is famous because it is one of the early "multimedia CD" games on PC, along with Myst.
I started 11th Hour as well, but got distracted and were even more annoyed by its cheesy TV shot acting and videos. Some games really wanted to be like movies, or at least TV-series' episode.