Very cool game! I love the 1 bit art style and the general gameplay loop. The one thing I noticed though was that the game was so easy I really didn't die until about 15 minutes had passed and I wanted to know what would happen, so there was really no incentive to upgrade anything. A general tip with the art as well is to consider pixel density as well, so something that's 1 pixel will always be 1 pixel. I noticed the enemies look to be just scaled up versions of the prior ones when you get further in. I think I got to around wave 15...not sure if the game is endless or not. Great job though!