I feel like this started out slow especially with us fumbling around in the first wave trying to find key bindings for things. I didn't figure out until the 5th wave or so that Q was self heal. I was switching to 4 and pressing middle mouse and often the switch time would get me bit because i'd be running around without my gun.
Kinda wish they had a big campaign to clear through, i mean frankly if somebody made a killing floor meets diablo game more focused around leveling and acquiring rare stat gear with no gear loss on death... well lets just say i wouldn't be wasting my time writing this comment.