Ugly redrawn shots (pic related)
Inferior (and plagiarized) Yamamoto music, later replaced with Kikuchi's in worse palcement than originally. Absence of the insert songs like Unmei no Hi when Gohan goes Super Saiyan 2.
Worse voice acting because Nozawa and rest are old
Removal of bad filler along with good filler
Didn't actually reanimate any of the worse episodes
Overall there's no reason to watch Kai unless you have a real bad case of fillerphobia (in which case just read the manga) or you want it in English since it improves on that dub