Improve mob pathing - let them go over logs and such like players do. Some balance work for weapons and shields. Let the block/zone run a bit after player portals out. Let bosses, at least, break through terrain. Make boss fights shorter but more exciting - like add some more attacks and randomize which set of three or four a boss has when spawned. Add some mobs that aren't weak to blunt, or for that matter elemental attacks.

I'm sure they'll eventually work something out.