Decent. This is very well polished and pleasant to look at but the gameplay had so many things that threw me off. First is the lack of variety with enemies - most you could reflect straight up to defeat. Many of the ones that sidled side to side were too easy to defeat as well; the balls I just reflected slowly, and they literally walked into the reflected bullets. The normal enemies that turned simply vanished and were no longer a threat after they turned sideways.
By far the most annoying thing about the game is that I could never really get used to how far up the map I could travel. Frequently my shots were sabotaged because of that damned limit. Please just draw a line over it or something. The game as a whole is too long and too easy - I didn't get a game over once, and I never even figured out how to use the bomb or the 'special' mode. However, the levels were frequently too long and monotonous.
Overall it's a very pretty game. The menu and game look very well done and the effects are nice too. It's just too bad that the game isn't challenging or as fresh as it was meant to be.