Finally finished wave 20 and completed the game! I needed to download the pc version since web lagged so much, but I do have a nice time after doing that! The game is very nicely done, the controls are very polished and smooth, and playing the game feels so good. It also got some good music to back the gameplay up too, nice work!
For some constructive criticism, I would really want to see where the enemies are, especially when they just spawned behind you. Maybe adding some sort of on-screen radar would be nice. Also, I think the bullets shot by the enemies are a bit fast and accurate and are quite difficult to dodge. Do they do predictive shots? I eventually resort to kiting enemies at an extreme distance in order to not get hit, and I guess that's not the intended way to play it. Also, I felt a bit sad not having anything to acknowledge the completion of the last wave, a good old "Game Completed!" screen would be nice!
Anyway, despite everything I've said, this is a very nice game! Nice work!