I Liked the game!
it was pretty fun, i'm just going to suggest a few things tho.
Suggestions:
Mute Sound Button
Bigger Maps maybe
Different Maps to pick from
A bit Better graphics.
Make the health a different color so you can see it better.
When in game an exit to main menu button
Here are some bugs I Found:
When you click upgrade, and try getting it off the upgrade screen by clicking away it did not work.
I did not find many actual bugs.
But overall i liked the game :) good work.