Long story short:
Got it, played it through, it was a let down.
The graphics are better, but three quarters of the levels are missing, and the added new bossfight is just crap.
there are also less monsters, and less type of monsters.
There's supposed to be a coop mode, but i haven't try that one yet.
I wanted to play coop on the military base level, and you know what? it's been cut too :(
I already wrote a reviw on mobygames about it, that sums it up:
http://www.mobygames.com/game/windows/painkiller-hell-damnation/reviews/reviewerId,224970/
I'd suggest black edition instead as well.