Not bad but not good either.
If you are a fan of the series you probably already have this game. But if you are not - avoid this game. It is good for multyplayer but it has no such great battle system as SC, Tekken or SF. When you play it single after 2-3 hours you will notice that missions start boring, supers has very long script-animation and they will freak you out scince they cant be skiped.
This game is also very easy to master. It is good for unexpirienced players but suck for experts.
Developers could make this game 2 vs 2 - this could work. Still I belive that Naroto series is best at beat'em up or action/rpg genre.
Diagnosis... Rent to play with your friend. Never buy, because there are so many great fighting games to play.