Neat little game, the art and music were well done. Could be a lot of fun if there was time to add some polish! It took me a couple of loops to realise what the upgrades were doing, at first I wasn't sure if they were just temporary powerups or if they were even having any effect on me, so some text saying what each one does would be nice. Also, maybe this was a symptom of short dev time but it was weird that the bullet speed was variable based on the distance of the mouse from the character, and the distance from enemies to the player. I think having set bullet speeds would feel better and more natural. Also sometimes me and the enemies managed to shoot through the walls. Some simple sound effects would also go a long way, but I understand that's not a high priority for things like this.
Overall I think it's a cool game with promise, well done!