I completed this game at 1:12 AM Central Time on October 22nd, 2007. (3 minutes ago!)
Although I beat it once a long time ago with the good ending (whenever a game presents moral choices I always play through as myself, or basically as what I would probably do if put in that situation, in this case, saving the Little Sisters), this time marks when I completed it a second time with the evil ending.
THE best single player campaign I have ever played, because of the magnificent story telling, sublime graphics, and sheer innovative gameplay; with gene modifications and great weapons. Only gripe is a lack of enemy variety, but everything else in the game is perfect. Goes to show how great a game can be if all time is focused on single player and not split on multi player.
Well, I got 25/50 achievements my first time through, playing on Normal. Which is really good for my standards. But yeah, probably the best FPS I ever played, definitely the longest. And it has so much replayability. And so much to do. Man, this game is awesome.