Kai, like full metal alchemist: brotherhood, is a remake that follows the original manga more closely. So the story flows quicker, less fillers which I hate. They also removed damaged frames or something like that from what I've read. And they were unable to get some of the voices back so they had to replace them... Which is a shame. What's even more of a shame is the only places that are showing Kai have done some editting of their own and cut parts out that they don't like or something >.< Stupid tv channels...
But yeah, i prefer the shows that follow the manga more closely, all the added nonsense gets on my nerves sometimes...