bioshock 2 actually improves as a sequal but keeps everything that made the first one great.
the level up system is quite similar to call of duty letting you unlock a variety of weapons, attachments, perks and plasmids. there are a variety of multiplayer modes that keeps the game feeling fresh and new. and in my personal opinon the multiplayer did something that no other game has every accomplsihed for me and thats have a great capture the flag mode. in bioshock its called capture the sister but the rules apply to any typical capture the flag but for some reason it works really well in this game.
overall bioshock 2 is a really great game. i would reccommend playing the first one before picking this up though but either way you will have an enjoyable experience