You made something really amazing out of this concept! The game looks really good (I will leave some tips on the end of the comment) and it sounds nice, I had lots of fun trying it out! I managed to destroy the final boss after 2/3 tries, each learning a bit more about how to counter its attacks!
I enjoyed a lot, you did great! XD
A tip:
I took 2 tries to notice the small blue missiles that the mothership uses at its second phase in the future, because they were a little hard to see..! Maybe adding a more contrasting colour would make it easier ;)