Interesting idea, I'm sure it could be interesting once you add more diverse content.
I did encounter some bugs very early on: I got stuck on lvl 2 because 2 blocks essentially became immortal (they would move and take damage, but never disappeared). Also, holding left click while spamming right click doubles or even triples your fire rate.
Also, perhaps don't let hitsounds overlap, otherwise they start crackling if you start shooting too fast.
Nothing that can't be fixed though! Keep it up!