This has for sure been one of the most fun games. It really sucks you in. I definitely feel like there are some balancing things that need to be tweaked but those are always hard with this type of game. For example if you get a few of the basic upgrades and then just focus on movement speed you can clear the level so fast all the other upgrades seem pointless.
I got to the point where I was clearing a map in less then a second, and rarely even firing at any enemies.
I still had a ton of fun playing and would love to see where this goes in the future! Great job!