Above is a Fleischer cartoon featuring Koko the Clown, the studio’s big star until Betty Boop (and the now largely forgotten Bimbo) came along.
One thing that really impresses me about the oldest Fleischer cartoons is how strong the line work is. In modern cartoons, lines are razor-thin and uniform in width, and don’t really have any personality. The lines found in the old Koko shorts, on the other hand, have an expressive, calligraphic presence. That this quality was achieved not in still illustrations but in the labor-intensive medium of animation is pretty remarkable I think. I can’t think of any modern animation that uses lines so artfully.