Cool music and solid sound effects. Attractive color palette, solid character design. Clear visual presentation with lots of great "game juice" (I particularly like the scene transition with the hangar doors closing and opening). Smooth controls with an authentic 8-bit feel. I was not expecting level bosses--and they were very well done, challenging but fair and with multiple weapons!
The modular ship mechanic has potential, but with only these limited levels the system doesn't quite have enough room to shine.
Minor quibble, but I was not a great fan of the way the text scrolls on the screen. Half-formed words will sometimes move position when they are fully spelled out, which I somehow find very distracting. I am inclined against revealing the text strings character-by-character... I never felt that added much.