I would say a 12 or 13. It was way better than the original. The only major letdown was with some of the new characters. I liked the characters themselves, but most of their special techniques were more like taking a break and letting their squad members attack. I hope in the third game (hopefully I can find a copy later today) each character has totally unique specials. All in all, though, it was still a good game.
I'd give it a 11. It wasn't as addictive as the first game, but it did have a larger selection of characters and stages and a MUCH longer story mode. I hate when the characters specials are Ultimate Mode or one of their teammates specials. However, I love the idea of Pest characters and the minigames. Also, the graphics could have been updated from the Japanese version's, but they weren't (or not noticeably).