I would never claim that early GT is good, but it sure is… well, something.
Ironically, GT Goku is characterized with much better continuity. When things are lighthearted, he’s got the old childlike joy, but when things start to get serious with Rild, he turns into the serious, competent Goku from the 23rd Budokai.
In Super, it depends entirely on the episode, but generally speaking, he just acts like kid Goku in an adult body, except it’s never funny, and Nozawa doesn’t sound charming when she’s playing a silly part anymore because she’s in her mid 80’s.