I have played it a few times. I didn't care for it that much. It was fairly fun, but got repetitive quickly, since you can lock onto your enemy and go into morph ball mode to get away from your enemy. That is all we ended up doing. The arenas were pretty uninspired, too. They were just symetrical levels that seemed thrown together. Perhaps with three other people, it would be more fun, because I only played 1-on-1, but I'm not sure.
It's no big deal that it's bad though, it's just an extra. The solo game is where the game shines.