This is the best PS2 boxing game to date, but given the competition, that's not saying a whole lot.
My take on this game is that it's a pretty good boxing engine, wrapped in a pretty dopey game. If you're into these anime characters, the backstory might have some appeal to you. For the rest of us however, since they're neither non-fictional nor exaggerated fictional characters, there's little to hold your interest.
Gameplay consists of just trying to beat one character after another, in order to unlock them. But there's no reason to work too hard to do this if you don't find these characters compelling in the first place.
The controls are pretty good, but can take a while to get used to. The analog stick moves the character relative to his orientation on the screen, rather than in an absolute fashion. For instance, if your fighter is facing you, and you want him to move across the screen to the right, you have to push the stick *left*, because your character will be moving to *his* left. Some might find this intuitive, while others might find it impossible to grasp.
There is also a problem in that as you move right or left, your character will frequently end up facing away from the opponent, causing you to punch air and leaving you wide open for attacks.
And it's probably just me, but I found that the opponents were able to move around the ring with a bit more quickness than my fighter.
Bottom line: a casual gamer will probably become very frustrated by this game, and see no reason to persist with it. A boxing fan, or a fan of fighting games and/or anime, would probably be motivated enough to become accustomed to the controls and eventually derive some enjoyment from this one.