They took everything that was good about Bioshock and added more including better combat control + new setting and story
I'm having a lot of fun with this. Bioshock 1 was the best, but this is definently 2nd in series to me. It's like they took all of the great elements from the first game and added new elements that are just awesome. The shooting for one has really improved from my point of view. It is a lot cleaner and aim is a lot sharper. The nevironments are better too. For instance I was getting lit up by automatic fire while crouched behind a wall with a metal fence and some cog like wheel trying to kill off a few enemies inbetween loading. I was able to target through the fence and through the smallest little holes in the cogs and take out dudes. I was like, "nice"! There is so much more detail like that in this new bioshock. Its like the environments are much more realistic and interactive than they were before.
Secondly, I really like the new character Booker. He is the perfect grey area that is left open for your personal story line. I already made some choices that Im sure will affect me negativly in the future because I was trying to role play based on the timeline of the game. This game is edgy for sure. Some deep, polarizing stuff takes place in the game where you have to make a difficult choice.
The only negatives that I have so far are the same negatives that I found with the first two. Too easy & too much hand holding (atleast you can turn off the big pointer arrow in this entry)! Im playing on hard, and its kinda hard, but not really if you have ever played a PC FPS. Just like the other two there is no real consequence when it comes to dying. I just think that this dumbing down of games like this is a shame. Console generation devs just love "accessibility". Except for the Deamon/Dark souls guys (good work on those two!. ...i digress.
As for the setting, one neat major difference between Colombia and Rapture is that when you start in Colombia you are constantly around normal people just going about their lives, discussing current events and the ramifications and sometimes hilarious consequences of "Vigors": Its like rapture before the fall, but somehow more wholesome. It is very period specific which is cool, and this fact also makes the advancements in technology (like in rapture) that much more awesome.. So when you play look at it thorough the eyes of someone in 1912, not 2013. Also, be sure to find out as much as you can about the story. The beginning is very Dan Brown-ish. I love all the references to Ascension and our founding fathers. Pretty detailed if you know a few things about obscure American History.
Enjoy!