Moving around doesn't feel great, I turn by aiming, but I can't strafe left/right at all. The aiming reticle is either not in the right place or projectiles are firing lower than they should be. You should either pause the game while I upgrade my stuff, or stop making it basically require me to take my fingers off the movement keys. Needs some sound.
Just to not be overly negative, I thought the weapon upgrades were alright and the enemy variety was good.