With work you could sell this!
Finding the balance is hard but its do able. I heard people complaining about not being able to get past the second wave because of the mine drains health mechanic., however I like that and after playing a few times you can really get going and it gets super fun!
I also like that just progression in the game isn't just more health more damage but different weapons', ability's (party time is the best) and constantly getting faster pace.
The only design problem I have with it is that you can use the shop when paused. As of right now if you took that feature away the game would be to hard but maybe longer wave brake time or the early game waves are easier.