A nice game, reminding of past games on NES, and even before. Levels are indeed procedural, and features basic IA for enemies, which seem to start chasing the player if he sees them. The difficulty lies in the horizontal posture of the ship, which forces the player to flee and position to shoot, which is nice for gameplay.
The style is very "game boy-ish", and respects the bonus theme.
I noticed a bug: if the game ends with game over, you die immediately on restart. Frustrating.