1. Cool character concept - ie. the whole 'possessed puppet' thing.
2. Cool moves. Geno Whirl, Geno Blast, Geno Flash, Geno Beam, Geno Boost... he may be kind of self-centered, I guess, if you go by the move names, but he has the right to be.
3. He can shoot pretty much anything out of his extremities. His index finger is a small minigun, his forearms are rocket-powered, he can fire cannonballs from his elbows, and - oh, what else? A sludge gun, as well.
He's just pretty much all-around awesome.