Bugs need fixing
The concept is wonderful, there's lots of ways to fight, upgrades, all that. The thing I don't like are the bugs. So far the only bug I've found, or noticed at least, is the unlimited upgrades because of negative money. It completely ruins the game play. Of course you can just make sure you don't go into negative, but we're humans. Gameplay is best when you must accomplish to upgrade.
Other than the bugs, the game is really fun. I'm giving you a 7 because of the bugs.