If you enjoyed BL and wished it were longer, get it.
It's not much of an evolution on the first game, it's just more of the same. The only significant change I've noticed is that the enemy AI is less stupid, they'll now flank well, and try to surround you.
Well, it's Diablo with guns. Depending on your point of view that's either incredible or tedious.
The PC version is actually a proper port with PC features built in to it rather than the first game which had a really poor job done. With a game like this, I guess the main factor is what platform your coop buddies are playing on, but you're not going to feel punished for playing on the PC this time around.