This was a really fun game. A couple of things i feel you could use to improve on it, is there is a lack of audio, other than the shooting and the spawns attack sound, which both where pretty loud and no options to turn them down in game. I would look at balancing audio as well as adding some kind of backing track, even at a lower volume to keep the player in the mind set of the game and keep the vibe and mood going.
The mechanics where really fun, though i did get turned around a couple of times playing as i started shooting the opposite direction of where my player was but once i got around that it was really fun to see how well I could do. made it to Wave 4 and started to get the upgrades. which did cost quite a bit for what was gathered at each round, some balancing of the prices vs money drop from the enemies will def help it.
Overall! This was a pretty solid first game jam entry and I can see this getting some awesome updates and being a cool game to see grow! Great work on it. taking that little bit of feedback to a second iteration I think you would have a pretty awesome game to show case!