It's just not the same... in a bad way...
The story of Bioshock 2 takes place in Rapture, as it did in the last one, and this time you are in control of a Big Daddy, a guy in a big diving suit. Your mission is to go and find a Little sister that you are bound to (nothing weird there), and kill her mother who has become a tyrant who united Rapture and has killed you in the past and so on. The story isn't really that interesting as it was in the first one and neither is the atmosphere. Rapture is no longer scary, especially since you are in a big metal armor, which was the main thing of the first Bioshock.
The gameplay has improved if you look at Bioshock as an action game. You carry your weapon in one hand and you fire your plasmids from the other. The problem about this is that this game, however easy the first one was, is way too easy. Sure you have new enemies, but you still revive yourself in the nearest vita chamber when you die, and the enemies still remain damaged. To top all that you are now dual wielding with stronger weapons and plasmids, plus little sisters can give you more ADAM this time so you can just go through the level with ease. Although it is still fun to toss splicers all over the room.
This game, even though with all its issues, is still a lot of fun. Sure it won't satisfy the hardcore shooter fans or the hardcore horror fans, but it has a lot of value in it so it is probably worth your time.
Pros: Fun gameplay, good sound effects, plasmids
Cons: Way too easy, lack of scary moments