I have pre-ordered it,too but for the PS3
I so love Bioshock 1.I played the Game 4x on PC and 1x on PS3,Its a great Game.I'm very curious about Part 2.
Edit Sunday:
Yeah The Parcel Sevice saved my Saturday.I got my Copy in the Noon and played nearly the whole Saturday..
Its pretty awesome and they improved many (kinda boring) Parts out of Bioshock1.
Some are:
1.
Youre now able to adopt the Little Sisters to find corpse that contain ADAM.
Also the Little Sisters handling is way better than before.Now you catch them and put them on your shoulders.
Besides of that you now can find ADAM Worms outside of Rapture in some of the numerous Underwater See bottom Sequences.
2.
Brute-Splicers
3:
Big Sisters.

They are way creepy-er than Big Daddys.
4.
Hacking is improved and much more fun to do and not so boring than in Part 1.
Now you have kinda of a weapon that can contain 3 different hacking Tools.
From Gameplay,really,it feels exactly the same than BS1.After not playing BS1 for a long time,i feelt like i would be back home xD Awesome Sequel.