Right before Teen Gohan goes Super Saiyan 2 in his Dragon Universe his first piece of dialog when talking to Android 16 is not voice acted and the second piece of dialog when he transforms into Super Saiyan 2 is in Japanese.
It's possible to glitch out of almost any stage in training by using either Kid Buu or Super Buu paired with Omega Shenron. By shooting Omega with 3 ki blasts staggered by quick pausing and unpausing and rapid replenishment of the ki gauge, you can lift Omega above the stage boundaries and over the invisible wall. From there, by having Omega attack the other character, you can teleport to have both characters out of bounds.
Yamcha will be instantly defeated if hit by a Saibaman's self-destruct move, in reference to how he died the first time in the anime.
This is the first game in the Budokai series to feature movie characters (Bardock, Cooler, Broly, and Gogeta), as well as the first game in the series to feature some Dragon Ball GT characters (Goku, Vegeta, and Gogeta are playable in their Super Saiyan 4 forms and Omega Shenron is also a playable character).
There are several unused voice clips that suggest that there were going to be more characters in Dragon Universe than there actually are. Notably, Kid Goku's Dragon Universe seemed to have involved him finding a time machine that takes him to the current Dragon Ball Z era, fighting Yamcha, Krillin, Tien Shinhan, Piccolo (who he thinks is still King Piccolo), maybe Vegeta, Teen Gohan (who thinks he stole the name from his grandfather) and Broly.