The first 20 episode were a bit slow.

Can't complain much about the animation since this is from 1979-1980, that's just how it works.

The filler after Rikiishi's arc were really good. (since after Rikiishi's arc, you actually need to jump to ashita no joe 2, continuing is optimal since it isn't "canon") I'd view the ending of ashita no joe 1 as alternate ending, though.