The first time you enter Rapture in BioShock you are totally enamored! There is so much to see and do you have to control yourself. It was a fully engrossing storyline and was Game of the Year for so many people for so many reasons. Thanks Electronic Arts! You have to hand it to a great video game!! The graphics, the music, as well as the storyline is top notch! No one would deny that it was a great game and you will be hard pressed when you play it yourself. There are a few things to point out between the two but we will narrow them down to two major differences.
The first major difference is that in Part 2 you are a Big Daddy protecting a Little Sister. This is a huge twist on the original because the first BioShock had you pitted against them as your major enemies. It was a sight to behold when you first saw a Big Daddy! I would have to say that the major difference was the storyline. You first got to rapture and had to figure out what was going on and did not have clear objectives but a main goal unlike BioShock 2 which has you in a very structured environment and you know if you Do not protect your Little Sister it would be no good. Any fan of great games will love BioShock and BioShock 2 so dive in and have fun!

In the first Bioshock your character's attacks were limited to either plasmids or weapons. In Bioshock 2 your character can use both, creating new strategic weapon combinations.

More plasmids.

Research is done with video footage in Bioshock 2, rather than simply pointing and shooting a camera in the original.

You are playing as one of the Big Daddies - thus, you have new gameplay options like harvesting adam.

Different story, same city. Bioshock 2 is a continuation of Bioshock 1 so the biggest difference would be the story.

Bioshock
http://www.gamerankings.com/xbox360/931329-bioshock/index.html

Bioshock 2
http://www.gamerankings.com/pc/945381-bioshock-2/index.html