When I first heard the announcement that they were making Bioshock 2, I was really skeptical. A sequel where you go back to rapture later and play as a big daddy? It sounded retarded and lame. I was ready to shit on this game like a ton of pigeons.
So naturally I was pretty shocked when it started getting good reviews. I picked it up not expecting much, and was blown away by how much I actually enjoyed Bioshock 2. The story actually makes sense in context, maybe even more so than the first game. I thought Bioshock 1 was a good game, but it had some flaws that I couldn't get over. The sequel addressed a lot of my concerns and delivered some fantastic gameplay as well as a good story.
One thing I disliked about the first game was how it was promoted as having "complex moral choices", which just boiled down to "Press A to be good or B to be evil". It was a super shallow and very video game-y contrivance for something with such lofty ambitions. Bioshock 2 still has these moments but also throws a curve ball at you, in which the choices aren't always spelled out. You will pause for a moment and wonder if what you just did was really the right choice.
It makes you think a little deeper, even once you've turned the console off. That's something that doesn't happen enough in games.