In a somewhat astounding bit of being behind the curve, I just finished "BioShock," a game which came out in 2007. I enjoyed the game a great deal, with its slowly-unraveling story and spooky atmosphere and gray-shaded morality. It's definitely a game that I can see myself revisiting, just to discover more of the story and get it all in a more concentrated dose. I was a little surprised, though, to learn at the end that the only difference made by your choices (spoilers, I guess) to rescue or harvest the Little Sisters was in the ending cutscene. I had a kind of hard time believing that, even if I'd harvested every one, Tenenbaum would have helped me along regardless. It's hardly a fatal flaw--the story is good enough that it doesn't really matter that the game is on rails, so to speak. I have the same feelings about the Portal games or the recent Batman games. Your choices don't make a whole lot of difference to the story, but the entertainment is in uncovering the story along the way.
So it's been a little bit of a shock to start playing Mass Effect (the first one), where I've heard that your decisions actually have major impacts on the rest of the story. I'm only fourteen minutes or so into the game, but I already like that the choices (dialogue so far, mostly) are more nuanced than BioShock's "kill the innocent little girl, or not?" Or even the "Jerk/Not as much of a jerk" dialogue choices in "Marvel: Ultimate Alliance 2." It has me really scrutinizing the options and considering the kind of character I'm trying to play.
Needless to say, I'm excited to be jumping into this series, and I hope the summer brings oodles of time to actually play it.