This game was fun to play and I love how the upgrades worked. Here are some bugs I found:

• After a while I figured out that even if I don't have the money, I can buy as many upgrades as I want. 
•  (Something minor) Enemies would sometimes walk into a wall and be stuck there for a while, then go back to following the player. 
• It was sometimes annoying how enemies would spawn at random locations everywhere, sometimes spawning right on my player and taking health off. Maybe you could use a slightly different approach to spawning? 

Overall the game was well made for 2 days.