Tron Evolution on the PSP is similar to the version on the Wii in that it doesn't really have a story but is just a series of mini games inspired by the game grid in Tron. They try to flesh in a story by saying your a program created by Kevin Flynn to be trained by Tron to compete in this tournament but really that's all there is.
Tron Evolution features many different mini game types, some such as the light cycle grid, light cycle races, disc arena and tank battles. There is one game type where you control a Recognizer and destroy tanks and turrets but the control is sloppy and uninspired. One thing that can be said about the whole game is that it is incredibly hard. It could be one of the hardest PSP games I have ever played. The light cycle races are almost impossible to win unless you've tried a million times and memorize the track but then it still comes down to blind luck. But don't let the difficulty scare you, the game can still be a lot of fun.
The highlight of the game is definatly the light cycle grid. This is classic Tron mixed with the new. Its a top down view of a square arena and there are four players on the grid moving in only right angles trying to survive long enough to make your opponents run into your light trail. This game mode is easily the most fun you will have with Tron on the psp. As you get farther in the game you unlock other arenas to mix it up. Another fun mode is the ligh cycle arena which is the same concept expect you move in a big arena from a third person perspective with full 3d motion and jumping to avoid your opponents light trails.
The whole point of the game is to earn points by placing first second or third in the games to move on to the next round of the tournament. Honestly there's not much incentive to do this other than to unlock the other light cycle arenas. Over all Tron Evolution on the PSP is a lacking version of it's console counterpart but is still fun for the light cycle enthusiast or nostalgists who just want a taste of old school Tron.