If you're not familiar with Xiaolin Showdown, it's a cartoon on the WB which frankly is pretty entertaining. The story is based around an ancient group on Xiaolin warriors whose mission is to protect the Shen Gong Wu. The current warriors in training are four students who are learning the ancient fighting styles, each with unique abilities. There is a villain however. An evil boy genius is trying to steal the Shen Gong Wu and use its powers, but the Xiaolin students must protect it. The story is interesting and there's plenty of character development take could be taken advantage of from the TV series, but for whatever reason very little of the charm from the TV series gets transferred to the game.
It doesn't help that the gameplay is lacking serious polish. Xiaolin Showdown is a basic action game with an extremely tedious structure where you simply attack enemy after enemy the same way over and over. Each of the four students do have unique abilities but there isn't much difference in how they are used. Other issues don't add any excitement either as you'll find yourself fighting the same types of enemies over and over.
Unfortunately, the graphics aren't going to help fill any gameplay holes. It's not horrible, but it is bland with little diversity in attacks or enemies. It is based off of the TV show with cel shaded graphics but it isn't going to help sell the game. There's not much to mention about the audio either, but it does use effects similar to the TV show as well.
Although there aren't any online features, Xiaolin Showdown does allow for up to four players to play at the same time. Since the gameplay always has all four students on the screen at the same time either as AI or other players, there's no split screen required which can be fun even in a game that has gameplay issues.
Xiaolin Showdown is probably better experienced on the WB then on the PS2. If you are a die hard fan, it probably doesn't matter how the game plays, but all others should be cautious.