I am playing DKS but I have found that to be a problem too, that enemies don't respawn and you also can't go back to earlier areas.Its very difficult to level up much past a certain point but I think I could get up to level 38 particularly by spending some more time in Broken Valley in the later stages after the defenses have been taken out, It would be interesting to see just how far you can level up before the final battle.
