How's (Real)Myst? It just got added to Steam for €4,99. I've heard a lot of good things about this game.
It's a very good update of the original Myst--the graphics are much improved, and you can freely roam the main island and other Ages, instead of being on a slideshow railway. (Well, you can go anywhere as much as the Ages' design allows--you can't go swimming. Or barricade hopping.) I
think some of the sound design may have been updated as well, but don't quote me on that. It's been a while since I played it. The puzzles and story are all the same as in the original version--for good or for ill, on the puzzle front.
(... ...I still have nightmares about that mazerunner.) They also threw in a small "bonus" Age and some little easter eggs for the series' lore buffs.
I'm not sure how compatible it is with newer OSes, though, so that might be worth looking into before you buy. It'll certainly behave better than the original Myst, though. FWIW, if compatibility is an issue, GoG has it for a dollar more, at least going by US prices, and that version should be a little more forwards compatible. (That's the version I have. I love Steam to bits, but when it comes to running older games on Win7/Vista, GoG has a better track record for providing proper support.)