Very good, lots of juice for a demo. Great sound effects, the asteroids breaking apart is really neat, and the controls feel solid. Didn't run into any of the jitter that the other comments mention.
Right now the asteroids feel underused, it would be nice to have a reason to break them apart for powerups or health or something. They also don't feel too punishing to crash in to, so the player can just kind of ignore them.
Minor nitpick but it would be nice to have the opening cutscene be skippable on retries.