It's... okay but it gets boring very, VERY quickly. I think it's just because the grind and the fact you restart at the wave you died on. There's no feeling of progression. I think if you restarted at wave 1 the upgrades would feel more powerful. But, even then, like another reviewer said, all the upgrades feel more like "sidegrades" or are extremely situational for what wave/boss you're on. And, again, the grind to keep your inventory stocked just kills it for me. If ammo upgrades, for example, were unlimited like the base ammo (but cost A LOT more to make up for the fact) I think it'd be 10x more fun and rewarding.

Hahaha, Dumb Aliens go die