I like the idea, but this game needs more player impute. It gets boring watching the maxed out house shoot 30 more waves of slow enemies. Perhaps let the player control the gunner, and implement new upgrades (Peirce, bullet velocity, house health, traps, etc.).
Upgrades prices are glitched. Sometimes the next upgrade costs less than the previous, or even goes into the negative and giving the player free souls. Bullet count price drops to 0 after level 40 or so.