Not as good as the original
In some ways Bioshock 2 is a better game than the original, the weapons and plasmids are way more powerful.
But the experience is lesser in almost every way except for the minor points.
You play a prototype Big Daddy who was bound to the daughter of Sophia Lamb. While Ryan was an objectivist modeled after Ayn Rand's ideals, Lamb is a collectivist in the spirit of Marx. She believes that the path to human success revolves around complete abandonment of the self and has restarted the little sister project somehow in service of that goal.
So you set off in search of your erstwhile little sister who's grown up in the 10 years since the end of the first game. You get a bunch of powerful weapons and plasmids to take out more powerful splicers. Back from the first game are the much heralded Little Sister choices. After killing a big daddy you're left with the choice to harvest or save the little sisters and it's basically a choice between more stuff now or more stuff later. But if you choose to rescue the sisters you need to take them to an Adam filled corpse and protect them while they drain all the adam from the corpse. Do this twice and then you take them to a vent and turn them human again.
I chose to save all the little sisters because that still makes me feel really good. Also really feeling good in the game is that while the little sisters ride around on you looking for Adam they tell you how awesome you are repeatedly. I know this makes me easy to manipulate but i loved it.
There are other decisions that involve slightly more gray area and effect the game's ending but I didn't find them particuarily special.
The game's ending was much improved over the original and rather than a lame boss fight it comes to a pretty cool climax late in the game. The story and the experience of seeing rapture again just isn't quite as special as it was the first time around.
The art style is still wonderful but it's not quite as effective as it was three years ago, the story has cool twist but it's not quite as awesome as the first one's "no agency" message, I could go on. The shooting is better but the experience is not.