its frikkin awesome man, darker than the first, hacking is improved but different, research camera is hugely improved, its more like a video camera that records you killing target, the more you mix up different weapons/plasmids the more you score.
Big Sisters are frikkin scary and nasty bitches (Darth Vader has nowt on their TK skills), the trap rivets are brill (and necessary to protect the little sisters when your harvesting Adam).
if you have the first buy it, if not BUY IT
