I love shmups, and I think the inclusion of machine gun convergence as an actual mechanic kind of interesting, even if I find it doesn't really do much. The lack of firing and movement animations for the plane and enemies stuck out to me, as well as the way the clouds would get in front of the camera. Also the clouds that have random lines through them, looks unfinished.
Also, suggestion, rather than having the enemies just rain down willy-nilly, it'd be a lot cooler if there was like a pool of patterns that the enemies to come down in and the game randomly selected from those patterns.