I really really like the direction you went with this game!
Our games have some elements in common hehe so we think alike
The level up system is intriguing and i like the rewards you can get out of it, though i gotta say that after wave 15 it was really hard to find motivation for playing since it takes forever to get to the next upgrade and the enemies become just too strong.
I decided to give up on wave 25 after seeing how long it takes me to take down one boss, and there were 4 at the same time xD
Overall i really dig the waves and i like the 3 different enemy types!
I could only wish for more enemy types and more upgrades to make it better