The gameplay is frantic, the music is excellent, the visual style and colour palette are gorgeous. The shift in playstyle from spacecraft to bike, to full-3d combat feels very natural; the currently-final mission (8?) is especially epic thanks to this. Little touches, like surf behind your ship when you touch water, or road-going enemies tumbling out of control when destroyed (during which time you can still shoot them to blow them up early!) really add to the visual spectacle.
I think there's plot but I was too busy juking to read it \_O_/