It's okay, just okay. The pros are the graphics and the audio, all in all the game is very nice. It plays very well during the first 20 levels or so, but after that the satisfaction is gone.
As the missions go by, the game becomes less and less interesting. I am nearly at the end of the gameplay, manage to get this far out of pure stubbornness, but this is very unrewarding.
Two major glitches that I've noticed:
1. The game sometimes "disappears" for no reason. I won't elaborate, since TheArsonist77 already mentioned this.
2. On several levels the boss was very chalenging, to the point where I just barely could defeat it. Problem is we sometimes both die the exact same instant (what are the odds?), and when that happens, the planet is cleared, but I am unable to choose an upgrade. Very frustrating.