It's good fun, there are some really fun weapons and enemies. Here are some suggestions for improvements:
-auto pickup weapons if you have no weapon, auto pickup armor if you have 0 armor, auto pickup health pack if you have less than 25%. Pressing the down arrow during battle is clumsy and also very annoying to accidently pick a stupid weapon that replaces your minigun if you were trying to pick up the health pack right next to it.
-the tequilla move is not all that useful: you can kill those zombies better with your weapons. With the tequilla move, the killed enemies don't count as combos that give coins, and it does almost no damage to bosses. Maybe let the tequilla bottles give money or some other bonus if your bar is full and you take extra bottles?
-Whether you can slay a final boss depends a lot on which weapons you happen to obtain during the last level. So if you have some bad luck of not receiving any good weapons and health packs during the final boss battle, you have to start over all 13 levels again to hope next time you'll have better luck... Your upgrades don't matter that much here. Maybe have some way to guarantee that you get some of your upgraded weapons during any battle?