Bioshock 2 doesn't has many new features, the single-player campaign of the original game was a little better.
It's fun to defend little sisters while they are harvesting.
Nice multiplayer mods.
Fun to play as a big daddy
Lots of tonics, plasmids, ammos etc.
The game is still very fun to play.
The ability to use weapons and plasmids at the same time is a nice addition
The Bad:-
Gets a little repetitive when you have found the right tonics and plasmids you need.
The core-gameplay is still pretty much the same.
You are the weakest big daddy to ever step on this planet, seriously, on hard difficulty you can be killed by 4 or 5 splicers so you never really get the feeling that you are a strong big daddy that eats splicers for breakfast
Story isn't that good as the original game.
I don't know but rapture has lost some of it's touch, like it's not that spooky anymore and nor is it mysterious like it was in the first game
Graphics: Nothing like crysis but they're still good. 9/10
Sound: The sounds are great in every way,the firing of the rivet gun, or the drill killing a splicer or a splicer talking to him/her self the voice acting is also very nice, everything is perfect 10/10
Gameplay:- The gameplay is still very fun and addictive, the online mods are also a blast to play
Bottom line:-
Bioshock 2 doesn't has many new features but if you loved the original or if you have never played the series then you should definitely buy it. If you did not like the original then there is nothing new in the singleplayer campaign but there is multiplayer that you may like. If you are not sure then I suggest that you rent it first.
Fearless Brute.