This is a very original concept, really cool to play, the artstyle is simple but still really cool, i feel like some music would be a nice touch, the upgrades feels very great and the ammo-farming mechanic is really cool, the only problem is that it becomes monotonous too soon, maybe some variety in enemies would make it better.
Unfortunately our musicians ran out of time for the gameplay music. I'm glad you liked the core mechanic!
I agree that more enemies would make it better, but I guess that's just jam games for you. I wanted to include an enemy that didn't hurt you but would attack your plants, things like that for variety, but having difficulty levels and upgrades ended up taking precedence.