Pretty neat to have flipped tower defense on its head like that !
I also like the full mouse only controls, this also makes for a good mobile adaptation later down the line.
My only gripe would be that the bullets in the stages you get shot at don't pop quite enough, and i feel it would be better to gamify them and have them colored bright and flashy for gameplay's sake.
other than that its solid, and it's fun, well done to you guys :)