Good.
These games are my favorite. Yours is among the top i've seen- ingenuitive, shiny, and new. But there are a few issues:
1. Only half the screen is useable. Believe it or not, most of your audience is mature enough to know when its safe to go up farther, into the enemy. Please let us.
2. The sprites for the bullets and the crystals are too similar. I suggest either using a consistant color for bullets/crystals, in order for the recognition of each to be faster, or to make them more blatantly different. Keep in mind that people never watch their ship while playing these games; they look ahead. Hence, when either a bullet or diamond gets close to the ship, its out of the corner of one's eye that he sees it. The identities of each must be very different to maintain easy recognition.
Other than those major issues, I didn't see much I didn't like. The sprites are wonderfully made, the music is very fitting, and even drives the game some. The enemies have creative patterns of movement and attacking. Overall, you did a good job with this.