This is an awesome concept, i love the sprite work as well, the little robot is very cute and marketable, your music slaps hard, your design is interesting.
It is *incredibly* exploitable however. One of the issues with picking debuffs is i'm incentivized to pick upgrades that provide the least interesting gameplay, since interesting gameplay is dangerous, and i found a few different exploits in your current system.
1) you offer "x modifier up" modifiers before i've taken the X modifier, for example Zone Movespeed Up, Bullet Rotation Speed Up, Bullet Aim Speed Up, Bullet Boomerang Speed Up. I was offered all of these before having taken their prerequisits (Zone Moves, Bullets Rotate, Bullets Aim at player, Bullets Boomerang) and i think only rotation speed did anything, allowing me a good 5-10 waves getting a basically null modifier.
2) bullets Aim and Bullets Rotate are in direct conflict, i picked up that one rotation speed up and my bullets began to slightly yaw to the right, and then i picked up bullets aim and... now if i stand still none of the bullets will ever hit me, aiming is calculated before the rotation meaning every bullet now just sort of lazily flies past me, allowing me to stand in the center of the screen and not move to beat the level. i got to wave 18 before writing this, at this point my best strategy is to pick up movement speed downs, bullet speed ups, zone shrinkings, and those aformentioned dead draws of "x modifier up" mods, making me fairly confident it would be a good 20 rounds before i had to pick something that would actually force me to move.
That's all to say this is a solid design that just needs more itteration and testing, you should be proud of your work and i'd love to see more c: