Bioshock. What can I say about this game that's not been said before... Not much really, it is a damn fine game and you really should play it. It's easily one of the best shooters I've played in a good long while.
That said I have to own up to something, from the start I thought I was playing an pretty average shooter. As the game progresses you suddenly realise how involved with the whole thing is and you sink deeper (pun intended) into Rapture. By the time the twist comes up I was in love with it. The way the plot is slowly fed to you via voice recordings you have to find yourself is brilliant and while I felt at the start that it was really bad way to convey the story it turned into one of the more involving stories in a computer game in a while.
I've heard one or two people bitch about the ending. The end cinematic is not the end of Bioshock, it is the epilogue. From the twist to the last fight is the end of the story and it is brilliantly told. If you've not played it yet or given up due to a shaky start, you really do need to play this game.