Probably one of the most difficult but also one of the most fun psp games I have played ever. It follows an original story featuring future trunks and his struggles against Majin Buu. He eventually gets help from the Z-Fighters from the present (post DBZ, but pre-Super), to help in defeating Majin Buu.
The battle system is an improved version of Shin Budokai, with a barrier system, improved chasing animations, inclusion of SSJ4 (Goku), Future Gohan (who is more tricky than present Gohan) and updated move sets for most players.
There is also a Survival and Tournament modes which are really fun to play. In Tournament you get to experience some interesting interactions between characters who have never really been near each other. My favourite mode is Dragon Click, which features all the music from Shin Budokai 1 and 2, playable at your leisure.
Overall a great game to have and a shame it hasn't made it to PSN.