Aerostar (USA, Europe) ROM

Aerostar is shoot 'em up for the classic gameboy. The games music and graphics are all top-notch and the game is fun. The soundtrack is catchy and the areas you fly through are all pretty (as pretty as you can get for black & white 8bit, I think).
Scattered throughout each level are power-ups with several weapons/shields to choose from. Enemies attack from the land and sky - you have the ability to be in either but only in the sky for a short time (by pressing A). This is mainly used to 'jump' across sea. If you're in the sky, only sky enemies can hurt you and likewise when you're on the ground but you're able to shoot at either regardless of where you are. A boss occupies the end of each level (as is the tradition with this sort of game). All the bosses are designed really well, both in appearance and battle tactics.
It's really an easy game to get into and if you use the power-ups to your advantage (especially the shields), you'll have a lot of fun.