I actually see the co-op decision as a plus with respect to Obsidian. Myself personally I like to play games like this with my friend, from start to finish, so actually the system works well for us. We're both of equal level, and the challenge is there because one of us hasn't imported an overpowered character with tons of rare loot. It makes the game a one hit kill fest while the other guy runs around being power levelled.
I can see the problem with this in one respect in regards to pugging, but the polar opposite also applies, it stops some random level 20 joining your game and one shotting everything, not that I can see why anyone would want to play a game like this with a random person anyway.
I do think that for online play and local PC play that they should have made a different decision in regards to the camera. Online each player should have their own screen, offline on PC players should be able to take advantage of Eyefinity (multiple monitors). I'm used to the camera style however seems I have played many games like this before.