This was a fun little game. It took a few tries testing out different weapons, before settling on the AR as the best for me. I got the Sniper just before getting rushed in the water dimension, so it was a really bad time to be trying that one out. The SMG and Shotgun also worked decently well for me, until I could get the one I wanted. I never tried the pistol as it seemed overpriced for the stats.
You have a nice base here, but the progression could be better. Early on the weapons felt too expensive, and I often could not get any until wave 5 or 6. Even then, once you finally can collect enough scraps in a level to get a new weapon, you are limited to the 2 options offered. It would be nice if the random selection favored cheaper options on levels where you are going to get fewer scraps, and also that other cheaper options are offered. Once I got the AR I was fine and used the basic version to finish the game on wave 11. The plant enemies that shoot were the ones I had the most trouble with, due to the large number of projectiles that slowly moved across the screen filling it up in places.