After a few more hours of Naruto: Uzumaki Chronicles, I can see that it's more than just a game that will please fanboys; it's a game for anyone who enjoys 3rd person fighting games.
2-player play in story mode may remind some players of old 2D brawlers like Double Dragon. Once the main player gets into a fight, the second player can press 'START' on their controller and join in on the ass-kicking. Player 2 can pick from whatever characters are available for that mission, but they can't change characters on the fly like Player 1 can.
While the action and fighting doesn't slow down because of a second human player, I did see a flaw in co-op play: camera angles. Once Player 2 steps in, the camera no longer can be controlled by either player. This may be the decision of the designers so that neither player will get disoriented or blocked by weird camera movements, but it makes it hard to see the whole battlefield sometimes.
I also had a chance to do a few missions in Mission mode. For someone who only has a limited amount of time to play video games a day, Mission mode is a good way to get instant gratification. Players can choose from a variety of missions ranging from "fight all the enemies in X area" to "catch some shadow ninja who's running around from village to village". The missions have time limits and it usually takes only a few minutes to complete each mission and get a reward such as items or money.
The best part is that since most of the fighting areas are small in Mission mode, the camera issues in 2 player coop don't crop up that often. Since any of the unlocked characters can be picked to form a team in Mission mode, I see that mode as the best choice to pick for anyone who just wants to get in a few quick minutes of ninja goodness without having to think too hard about the plot, but still want to make progress toward the main story.
