A very good game, but definitely lacking in areas.
There are many ways to play N:UNH, the first and foremost being the Heroes Mode. This involves your team (a pre-selected or customised team of three different characters) battling through a various amount of stages, depending on the difficulty your playing on. You're rewarded with additional characters, as well as points, scrolls, and addiontal material, such as movies. However, it lacks a story, which is sad. It almost makes sense, as it is set during the Chuunin Exams, which leaves little room for improvisation; but, one can't help feeling that the lack of a proper story really lets the game down.
After Heroes mode, there are game modes to play against the CPU, which earns you points and scrolls. It also allows you to use any characters you have levelled up, using the acquired points.
Additionally, you can fight against human opponents in the same manner. A nice bonus is the game-sharing option, which allows you to play with a friend who does not have the game/
The last way to play, is to do missions, which are unlocked via the scrolls. This is were you fight against the CPU, but are given specific win conditions. These let you unlock points, as well as go up ranks, which can be shown off to your human opponents.
There are few things wrong with N:UNH, bar the lack of a story mode. The fighting is fun and easy to master. There is a wide range of combo attacks as well as special moves. The battlefield can be taken apart, piece by piece, to reveal items and pseudo-easter eggs.
The loading time seems to be a huge problem for other reviewers. I admit, they are frequent, but they are over very quickly. They are not as bothersome as others would have you think.
The only other major gripe I have with the game is the cast of characters. Twenty characters is a lot, but the game lacks various key characters from the Chuunin Exam arc, which I find to be almost unforgivable. No Kankuro. No Temari. No Kabuto. No Dosu. No Zaku. No Kin. No Anko. Hell, even the Fourth Hokage and his grandson could have been thrown in with little consequence.
Ultimately, this game scores a solid 8.5/10. Perfect for Naruto fans, fighting fans and anyone with a few hours to waste.