I have it. It's fun but it's completely broken.
It's probably one of the most unbalanced fighters I've played. Don't expect it to be a competitive type of game. The fights are very spammy.
But, like I said, it's still fun. Once you get used to the combat, you can start to take advantage of the system.
I would recommend it to One Piece fans, but don't expect it to be as refined as something like Naruto Ultimate Ninja Storm.