My fiancee and I have just gone through Myst (4 days) and Riven (5 days) in one straight shot, and now I can honestly say that I've become a fan of this type of game. It's almost an addiction, you get these insanely hard puzzles and when you finally figure them out and beat it it's a huge rush of exhilaration. Oh, and the endgame to Riven? You don't know what to do and there's apparently 5 different ways things could go wrong...
Ahhh, now I'm out to look for more of these games that I tried and failed at earlier in life. 7th Guest/11th Hour... I remember one that was very weird, it was sponsored by Learning Channel or maybe one of the more "Intelligent" developers, there was the narrator that sort of helped you along, and then the bad guy would appear as the screen went red-tint and played this scary-ass music. I played it when I was 15 and it still freaked me out.
Return to Zork and Zork: Nemesis fall under this, as does "9" and many more that I suddenly want to play. Oh, and Myst III: Exile...
What do you all think about this genre?
-AG