It's very fun as you get to the later waves! The variety of enemy patterns makes the game more and more interesting as you progresses. It's great that you can also restart at the current wave instead of restarting from the beginning.
Two things I would change:
- Maybe you could add the "shooting butteflies" early in the game. During the first wave, I wasn't really getting the point of switching from bee to butterfly as the enemies are quite slow and easy to shoot. That becomes more clear once you get the bullet hells from these enemies.
- The animation when you have only one heart left obstruct the screen a little bit too much in my opinion, you might look for a more subtle effect.
Overall, I really enjoyed it. Thanks for making that game :D