I just got Astroboy tonight, and have fired it up on the DS. (The Omega Factor one, not the PS2 one.)
What a game! Treasure definitely knows how to make a game. This, Contra, Radiant Silvergun, Gunstar Heroes, etc.
This game is right up my alley. My question is this: any more suggestions on games just like this? Little (or big) unsung heroes that I might have missed?