Originally put off by a review which described it as a series of puzzle rooms, I finally picked this up based on word-of-mouth. No game has a better opening where simple controls and music combine into what was a near religious experience for me.
It's a 3rd person action/sneak/puzzle game with a gloriously fun collection mechanic, backed by one of the best soundtracks in a PC game, great voice acting and a touching if cliché story. With a sequel FINALLY in the works (following a pretty poor "to be continued" style ending) you owe it to yourself to play the original now.
A genuine gem.