The gameplay was very smooth and the types of zones you flew over changing kept it interesting. Also I feel that the enemies matched the zones perfectly, save for maybe the third boss, I can't put my finger on it but that one felt a bit off. It's probably just me. Someone already complimented the auto-fire, and I concur. It was a good idea. Dodging and aiming was enough to do, and with this kind of game you'd just be holding down or mashing the fire buitton anyway. Music was cool, graphics were very SNES starfox-ish minus only the length of the game and a story. If there was a story I didn't read it. You don't need one for these old-timey shooters. I do have two suggestions, but they wouldn't add much to the game.
1: Bombs: limited: wipe out all enemies on screen. I'd make them hard to come by and only able to hold one at a time in cargo, separate button.
2: homing missiles or lasers or whatever, weaker than standard weapons by about 50%, uses auto-fire, but using yet another button can be turned off to naught but regular weapons again.
Like I said these are not really great suggestions. But I do think they would boost your game's dynamics.