Ok not bad. New fighting system, though. Hey, you can learn, right?
Good: Janemba, Baby Vegeta, and Bojack, are playable. New Z-item system. More life-like. New "favorite techniques". Charge your opponent after you make them fly in any direction, and smash them down, up, left, or right. New attacks called "rushes". Attack repeatedly with ki blasts then end with a charged ki blast...(or a special move!). Battle with charging duels and special ki duels. New ultimate battle option at the main menu. Improved story. alternante stories, like Budokai 1! False "Super Sayian 2" finally realized as "Super" Vegeta or Trunks.
Bad: Broly and Cooler only in final forms (excluding meta-cooler). Ultimate Battle 15-1 so hard you have to cheat. You must wait after starting ki charging for ki to grow. A "they didn't try" moment: Ultimate waves (i.e. 10x Kamehameha) still explode like spheres (i.e. Big Bang Attack). All you get at World Tournament is 1 z-item. Choose your form wisely: thats that for the rest of the fight.
Other: Dragon balls in fighting stages! Music random instead of 1 song on 1 stage.