I never played this game in its heyday. I picked it up during the sale and spent this past weekend playing all the way through it, because even though I'm not a huge adventure fan, I like games that try a different angle on the genre. Sanitarium does this from start to finish (and man, the last two areas of the game are AWESOME). The easiest thing to say is that this game is a mindf**k. From one section to the next, you will be asking yourself "what just happened, and why?", but it is tied together nicely by the end. The visuals and ideas on display are astounding.
I thought the protagonist's voice acting was really bland, and sounded like a guy recording in a studio instead of a character. That, and the frustrating stair climbing movement controls got a little annoying (just the stairs...the rest was fine). I admit that I cheated on a couple things, mostly because I failed to fully explore an area or just didn't see something, but there are no puzzles in the game that are all that hard.
Actually, now that I think about it, the whole "revelation" part is never really explained....oh well.