I have played about 30 minutes of this and reached level 15 so far. Base concept and mechanics are solid and fun. Music is great, visuals are clean, I imagine you will want to add more songs eventually.
Tutorialisation works naturally and is fun although you might want to add a "click to shoot message" or something along those lines. It did not take long at all to figure out what to do, it kind of depends on how user-friendly you want it to be.
I don't have any serious criticisms, this is a really solid beginning, but you may want to keep the really simple levels going for a while longer once you begin putting together a completed product. Difficulty ramps up quickly. I think it would be interesting to see horizontally longer levels as well, something more akin to a platformer, here and there in between the "puzzle levels". Levels where it is harder to fail by falling and with a few more enemies added perhaps. I will finish the last levels soon too, I got angry at one and had to leave the game alone...