Got to round 9, I think...
I really liked the fact that the player is in control of their own difficulty curve, that was really neat and kiting enemies into weapons is always fun. Maybe it was too early-game, but I think one more vincible enemy type would have made it really addictive.
I have to agree with other comments, the homing missiles and the arrows were a little slow, particularly to enter the arena. Zombies were a good pace though and the Golem moving relatively slowly felt fair and balanced too.
Congratulations on the submission, and a solid one at that.