Fun game, until it becomes impossible to win. Some of the asteroid spawns felt like they couldn't be beat.
The asteroid hit-boxes were a bit bigger than the sprite, it seemed. I think the hit-box should not cover too much of the back of the asteroid so you can slip past them easier and overall the hit-box should be a little smaller than the sprite itself.
The music would play on top of itself each time the level restart. By the fourth restart I was hearing a garbled mess of multiple versions of the same music looped on top of each other.
Pressing space to toggle your direction gives the player less control but I think makes for a more interesting experience because more thought goes into where and when to toggle instead of the second nature of up and down keys.
Overall, a decent entry. It would have been a lot more nice if the difficulty was a little more reasonable.