Fun but could use polish
I've sadly played more then enough games of that type so I couldn't supress a little *yawn* when I found out this was another one. But as far as I can say your's has been one of the better ones. :)
Doesn't mean it couln't use some more polish:
I really missed a fun reward for kiliing multiple enemies in one hit. Display the kill count, play some "Momomonsterkillll!" sound or give a score bonus. (I realize the score multiplayer is supposed to do that but changes in the fractional part of a number seem not very thrilling! ;)
Also, I found the upgrade selection screen pretty confusing and never really figured out some of the powerups: Like the satanic rune thingy.
Lastly I might not have played long enough to reach different enemy-types but I guess a bug infestation is the most boring army of foes I can imagine. No offense meant but that mix of Starship Troopers with Starwars just doesn't work for me.