Zombie Boom!

I feel like this game needs a little more than just arbitrary upgrades. It would be interesting if maybe you would start out with just one shooter and worked your way to get the other 2 maybe; along with other upgrades maybe like rooftop shooters that could be a button on a cool down? There’s also no clear line as to when you lose if a zombie gets too close and there’s no real penalty for losing. Also the boxes that drop are hard to tap sometimes because I had to drop a bomb and the tap the box. Seems pretty inefficient.