Damn, just imagining the intro Yahtzee described makes the actual intro feel so lame....
But regardless, did you ever expect Bioshock 2 to be better then Bioshock 1? In the story/characters departament, that is? Bioshock had (and still has) one of the best stories in video games, probably the greatest setting and, hands down, the single best supporting character in the history of forever ("I want to take the ears off"..). Could you really expect Bioshock 2 to top that?
No. Just like there are never any good sequels to great movies (or games that put emphasis on the storytelling first, action second), Bioshock 2 couldn't possibly top the first game's storytelling. And if you expected it to, you were most definetly disappointed.
But, where movies don't have anything else to offer other then the story, games have gameplay (duh). And that's where Bioshock 2 shines. It is better then the first game in every single aspect (of the gamplay, mind you). Plus, multiplayer never hurts. Combine that with a pretty good plot of it's own, and you get a game, that might not stack up to it's predecessor on the "greatness" scale, but a great game non-the-less.