It felt a little slow to me. I noticed some other comments saying this, and your replies about it being a tutorial for the player. It's definitely hard to find the balance, since you don't know what sort of person might be playing - you could make it faster, and then it would be too fast for some people. I would've liked a faster firing speed, like twice as fast (even if it did less damage), since the firing speed felt frustratingly slow. And some kind of visual or auditory (or both) indication that the laser was ready to fire again.
I liked Mr Worvin floating across on a cloud for upgrades. I liked that you could hit several of the fuzzies at once and get a combo if they were in the same spot. The art, animation, sounds, and music all went well together. It's cool that you made it in Scratch. 🙂