Bottom line: This made me an Astro Boy fan.

User Rating: 9.5 | Astro Boy: Tetsuwan Atom - Atom Heart no Himitsu GBA
If you are a fan of side scrolling, old skool pwnage, you MUST own this game. Treasure is already known as a great developer, and this game only solidifies their reputation. Astro Boy: Omega Factor captures the look and feel of the series and makes a great game. The levels have a wonderful ammount of variety, and all of them are action packed. The game uses a nifty RPG-like system of leveling up by allowing you to add to you're stats by meeting people and improving Astro Boy's "Omega Factor". The bosses are also a high point, and each one is unique and fun. The game may seem short once you beat it, but you'll quickly realize that once you play through it again, it isn't the same experiance, but it still maintains all that was good about it the first time through.