cool, the base is there. I like the tiny scropion sprite.
Sound is ok.
the biggest complaint i would have is that there is no "middle" enemy, the big ones are bullet sponges and the scorpions are one hit. would be nice to have something in the middle which dies after 3-5 shots.
I miss an xp bar
other than that, more upgrade types, different weapons and so on. of course more monster types etc.
well done!