Not that bad.
The biggest complaint I have graphics -wise were the explosions. The line type explosions didn't match the rest of the game's style, and ended up just looking hokey.
Gameplay-wise there were a few things. First, the bounding boxes seemed a little to large. I know I sound like a sore loser, but many projectiles seemed to impact far from their targets. Second, some way of registering an impact would be nice, perhaps the ship should flash, or the bullets have a little splash when they hit. That goes for both the bad guy's and the hero's. It took me a while to realize I was actually damaging the bad guys.
As for the sounds, the music was good, the sound effects were good, just switch the volumes. The sound effects need to be louder, and the music quieter.
In the end, it's not a bad game at all. In fact it could be a really good game.