My first run the game crashed on me when I was about three waves from the end, though I beat it the second time.
Other than that, though, this was a lot of fun and quite creative! I like how there's still time pressure as you get into the game's final rounds, which makes it feel engaging even when you have such an overpowered arsenal by then.
Honestly, I'm not sure what to suggest to improve the game visually. Maybe make the main character's sprite more detailed? Like, I look and the title screen and think, "dang, I wanna play as that guy" because it doesn't really feel like I am.