My brother and I played the game for around 3 hours last night. It was a blast.
The only real issue is that if you're not the same level as your friends it'd be very tough to play with them. Taking on level 10/11 enemies was brutal at level 7. We had to run and do another quest to get to 9 to handle it.
Of course this is early and our gear still is crappy at this point. Well
my gear is crappy, Aeacus is another story. I didn't find a purple level 13 machine gun or another blue machine gun in the box immediately afterwards. *grumble*
Seriously that purple machine gun does as much damager per bullet as my current sniper rifel
.