The gameplay has a few fundamental differences from Smash Bros:
"the scoring method has notable differences. Attacking foes fills an AP bar at the bottom of the screen, which grants three levels of a super attack once filled. You can attack an opponent all day, but the only way you'll actually score a point is if you KO them with a super attack. Level one attacks are usually limited, such as Parappa's spin kick. Once you get to level three, however, you're almost guaranteed a couple of points with screen-clearing attacks. Parappa breaks into a rap performance that annihilates nearby opponents, while Sweet Tooth transforms into his robot form for an insane damage boost.
Considering the importance of super attacks, managing your AP becomes the focus. Items like rocket launchers and the Spear of Destiny from God of War will occasionally drop onto the battlefield, and they can be used to reduce the super meter of opponents. AP orbs can be granted by certain moves, such as Parappa's Boxy Boy boombox ability."
Either way, I think it's silly to get caught up in this looking similar to another game series.
It's a win-win for everyone, if it's bad everyone gets to laugh at Sony and point out how superior the original Smash Bros is, if it's a good game, you get two great crossover brawler franchises instead of just one.