A very different game to be sure, especially minus the theme, though the game has it's own theme sort of which is interesting and at least fits MS Paint. There's also a decent amount of enemy variety besides just health, of which I didn't see too many that changed their health anyway, which is both good and bad?
The power ups system is a little unexplained, especially the way it switches and the amount counts, etc. Most of the time I just used the default weapon and hoped for a shield so I could be able to survive a hit.
Speaking of that, the game is pretty punishing not having any sort of health, and not being able to move in any way with enemies coming from all directions. Though I did manage it somewhat it's definitely pretty hard depending on the enemy spawns you get, sometimes you just.. die. Too much stuff to shoot.
A decent game overall. To finish off though there is a really big bunch of lag I believe from the particles that made surviving more enemies near impossible for me since I was unable to fire more than 2-3 bullets before everything started lagging out. Otherwise though, it's definitely a nice base with the weapon variations and such, I do feel like more ammo for them would be nice though, it would make them a lot more usable.