I really like the overall ship design and pallet, there is one thing bugging me tho.
The hull of the ship seems to be at a slight angle, but the cockpit and gun turret thingy are at a sideview, so it apears the hull is leaning down well everything else is lined up with the player... that looks kind of broken, perspective wise.
I would keep the hull, rather then scrapping it, and make an angled version of the turret and cockpit, then use them all together for when the ship is moving down, and then make a new version of the hull at a side view that lines up with the cockpit and turret to use when the ship is just flying straight ahead (so if the its NOT moving, assuming this is infinitely scrolling,) followed by another version of all of them angled in the opposite direction, for when you are flying up.
If you are feeling lazy, or trying to do this in one frame, however, just make the hull sideview, as that perspective will make more sense with a constant forwards motion.