Eh.
The triangle enemies are super-cheesy--in the later stages, if you're the right color they can pass right through you, but if you're the wrong color they can hit you without even touching you. I realize you needed some way to make the game difficult, but letting the computer cheat is just lazy programming. Besides that, there were multi-colored clusters of enemies that were too risky to bother taking out, so the later stages tended to devolve into dodge-fests rather than kill-fests.
It's really annoying that the tutorial texts pop up every single game. You only need to do that once.
After playing a few games it inexplicably stopped giving me any bonuses at all--I never got any more shields or bombs. That's basically a game-killing bug, and is when I stopped playing.
The graphics were really well-done, admittedly.