Good start, but there's room for improvement...

Hey, I just played the first level and some of the second. Good job!
I really liked how you flipped the whole world upside down! That was a good idea!

The game is creative, and fun. What you desperately need are some good custom graphics. Mainly for the tilesets. Which, did have some line breaks between them. You might want to fix that.
I think that when you hit B to turn on the lock-on thing, it should stay locked on until you (the player) turn it off. I seemed to turn itself off once all the enemies were out of the screen.

Anyway, its a very good start. I hope you continue working on this!
Good luck!