Dark Fall: The Journal for PC was pretty scary when I played it, though the puzzles are a bit obtuse.
Also, seconding Syberia, though I haven't played the sequel yet. I've seldom played a game with such endearing characters before.
"'Casual games' are something the 'Game Industry' invented to explain away the Wii success instead of actually listening or looking at what Nintendo did. There is no 'casual strategy' from Nintendo. 'Accessible strategy', yes, but ‘casual gamers’ is just the 'Game Industry''s polite way of saying what they feel: 'retarded gamers'."
-Sean Malstrom