It was alright, but there are MUCH better platformers out there that are harder, smoother, and even still in pixel style. I'm talking to you, Mega Man 9. It's interesting, but I can't say that it stands out in any awesome way. 3/5.
For a sequal, some kind of multiplayer eaither co-op, PvP or both would fit perfectly. You could have one guy leading each army.
Or, as Joe said, have some fighters that you can give simple commands to. like, Protect the Testudon. After all, who's commanding this fleet anyway?
Decent, needs to be a bit faster paced; faster ship and faster enemies. Also more enemies. Everything needs to be smaller so you can fit more enemies.
Otherwise, most boosts would be technical, the graphics could look a little cleaner. More powerups would be nice but not necesary, but at least say a point boost or exp boost.
Still, I'm glad you didn't just upload a crap game for a 'D' and points, this game is decent, especially for a first upload. I'll give it a 3/5 for now, but It's still a work in progress. Keep up the good work!