I like the idea! I had a hard time playing it - probably due to my lack of skills. It might help to add some gradual difficulty progression, maybe based on time survived or number of enemies killed. For example, later waves could spawn more enemies and increase the percentage of stronger (higher HP) ones.
I’d also suggest adding some power-up items. One idea: when picked up, a circle appears around the player for a short time - any enemies that touch it are instantly destroyed, and any bullets that hit it bounce back in the opposite direction. That could add some nice variety and strategic moments to the gameplay.