Cool idea, I think it takes a while to ramp up in difficulty, but once it does, it becomes pretty intense. I think in the first few minutes the pace is a bit too slow since the enemies are still relatively weak depending on what you choose. I also feel like a movement mechanic of some kind would really add more strategy to the gameplay. However, I like that you are presented with choices for what to upgrade, it requires some thought based on what you have already chosen. The sprites look awesome, I think you chose a great color palette for your game! Nice work!