Cool game! Some suggestions:
* Adding more powerups
* The green-charge-up energy ball for the interceptor could be activated with another key (e.g. right mouse button) instead of it interrupting the main gun. It could even keep draining energy as it gets stronger, inflicting more damage.
* There could be a selectable upgrade every X number of points (stronger weapon, more shield capacity, faster energy recharge, etc)
* A wider screen (and maybe taller) would make for more strategic maneuvering. This could be further enhanced by adding things like cargo ships (don't attack, they only drop pickups) or obstacles (e.g. asteroids).
* Adding a pause button
The graphics, sound and music are cool. I like the bomb effect and the lasers as well. Nice work overall, but could improve a lot!