I've beaten the game twice on each difficulty every year for 3 years since I got it. Thats how great it is.
Astro Boy Omega Factor follows Astro Boy on, to put it lightly, his journey to create a safe way to robots and human to live together in harmony, and find out who he really is. Seems kind of cheesy, but once you play it, you will realize there is nothing even remotely resembling dairy about it. I could go into more detail, but I'm trying to refrain from giving spoilers.
The game play... words cannot describe it. It is fast, smooth, and surprisingly elegant, with some slow timing. Boss battles are extremely fun, and they are not exactly pushovers, so when you find yourself beating one, you might actually cheer out loud.
The sound is what you would expect for a gba game. So not much detail required.
One thing i did not mention about the story is the omega factor. This is one of the best things in this game. Throughout the game, there are Tezuka's characters, from Astro Boy, or other series that he made. Some are hidden, some aren't. Kinda exciting for fans but not for other people is probably your first though, and it was mine too. Then something really interesting happens. A menu pops up with 6 options on it. These six options are entitled jets, life, sensor, laser, punch, and shots. Then you realize, every time you find a character, you get to upgrade one of these six. Not exactly your fable, or morrowind RPG, but it is so original, and i just found myself, playing levels over and over again just to find characters.
BEST GBA GAME EVER THAT I HAVE PLAYED. And if they made a remake of this game for say... the 100th anniversary, i would pick it up in a heartbeat.