Bioshock 2 is the a sequel to Bioshock 1 and is set in Rapture several years later where you play as a new main character in the game. So here are my thoguhts on it.
What I liked
More slots for plasmids and gene tonics- You can now equip up to 8 plasmids now for way more tactical flexibility. Compared to the 6 of gene tonic slots in Bioshock 1, you can now store up to 18 gene tonics making the game much more fun. The plasmids and gene tonics are mostly the same however although there are some new ones.
Plasmids now charge- You can now unleash more powerful effects with plasmids such a chain lightning with your plasmids when you charge up.
Glowing plants and water sequences- A lot of sea plants have invaded Rapture allowing the artists to go crazy with adding all sorts of crazy stuff. I also quite enjoyed the water sequences which allowed them to make it feel like you're underwater.
What I didn't like
Walking around in water is boring- Because you're a prototype Big Daddy you can walk around in the sea which I actually kind of like because of all the cool plants and sea life. Unfortunately you can't actually do anything except occasionally pick things up and getting from point A to B. I wonder if there was as better way to integrate the water and ocean travel in the game. Wouldn't it be cool to actually be able to use your ability to travel in water to ambush enemies or flood areas to kill people?
Too similar to the first- There are a few game play changes such as hacking being easier and harvesting ADAM is made more complicated since you can adopt Little Sisters to extract ADAM from special corpses. But otherwise, the behaves exactly the same as the first game with almost the same enemies and plasmids.
Morality system- This ugly feature once again rears its head. It just doesn't feel required in a game like this.
Lack of enemies- Once again the game fails to bring anything imaginative to the enemies beyond the typical humans.
Lack of controller for PC- For some reason you can't use the controller in the PC. I really missed the ability to have rumble. Recently they did update this in October 2013 but its still disappointing considering how old the game is.
Bioshock 2 is still a very fun game full of interesting ideas etc. It's biggest problem as other reviewers have noted is that Bioshock ended with no real need for a sequel. This game just feel unnecessary from a story perspective and in my opinion is more of an expansion pack than a proper sequel. I enjoyed the game and as long as you treat is as an expansion pack, so will you.