I really like these rogue-like wave type games. I was able to get to wave 5 (first one after the boss) before the shop-button failed to appear, and the variety of power-ups & their rarity make for great replayability.
One thing i found though, the boss was quite easy but also super long because he had such high HP, maybe balancing it out a bit to have a shorter, more intense fight would be nice.
Anyway, great entry overall!