Nice!
The customization features on this are super fun ! It's awesome to encounter a tough level and then have to start tweaking your armor/engine/weapons to get the right combo.
I'm not sure whether you'll revisit this game or make another one, but I can think of few little design enhancements that would improve the arcadey experience. It would be fun if there were little positive reinforcements when you get more XP: like when you blow up one of those tougher enemies or bigger asteroids, the font showing you your XP could be bigger and brighter, or it could have some flashy effect, or it could make a cool sound effect like when you get a big combo in audiosurf.
Another fun feature would be XP or Gem rewards for defeating specific chains of enemies -- it's always exciting in shmups when you feel compelled to take out the entire row of baddies even though you're scared it'll get you killed.
Anyway, congrats on putting such a solid game together!