Finished the single player last night... this is now one of my fav games. There is a lot more story and character development than portal 1. (well portal 1 had pretty much no story). The game is much more challenging than the 1st, literally i was scratching my head at some levels.
Also if you buy portal 2 on ps3 you get it on steam (PC) for free..... Hate myself for having an xbox right now. :(