Good, and simple (bad)
Fellow user goloerel pretty much highlighted the things the game lacks, though I would like to mention that getting a Max Power power up and going, for lack of a better word, momentarily insane and trigger happy never got old. Though also, at many points throughout the game, getting a power up often signified the difference between life and death.
For example, in the 9th level, near the end of it, no less than 4 of the big purple ships, 3 or 5 of the fuel containing ships and dozens of the blue, red and yellow ships were swarming me, and more were incoming. I was struggling slightly, nearly half my life gone, until, by pure luck alone, one of them left a MP power up behind. All it took was one single shot, and the galaxy lit up with a powerful burst of light. No more enemies.
Then, on the last level (normal mode), I was left shocked (O_O WTF HAX like) at the sheer size of the monstrosity that was the last boss. I took care of a few ships coming in on the side. Guess what, an MP power up! Big Bad Boss, meet my ultimate cannon of infinite energy. One massive energy volley later, and the remaining things on the area were a few stragglers.
So yeah, it depends on luck later on.