It was a different enemy type the two times I attempted it. First try it was demonic enemies, and I went down in the second wave. Second time it was a mix of mostly undead enemy types, and I got to the third wave and had only two enemies left, but lost my cleric and my mage earlier in the round and the two enemies that were left were highly resistant to physical damage, so I could only chip away at them as they pounded my fighter and ranger.
I think I will gain another level or two on my characters, then buff their equipment a bit and use a couple of potions pre-battle, all of which should make finishing the third wave a lot easier.