Level 9, still loving Borderlands. Found a few flaws though:
AI kinda sucks when it comes to attention span. They immediatly target the person who is hitting them, so if you are whacking the enemy constantly directing their attention on you constantly whilst your buddy stands by their side shooting them in the head with a shotgun which causes them to do like a backstep animation so they won't attack, they pretty much dont have a chance. We did this to beat Bruiser at like lvl 4.
You can also take advantage of the attention span issue when your buddy is down, you can heal them as long as they make sure all the enemies are attacking them.
And finally, you can get behind some cover with your friend and whilst you duck let your buddy stand up and peek over the edge and get shot by the enemies until he goes down, then you heal them, get a quick 100XP and then repeat. 100XP is nothing though so it's kinda okay.