Cartoons in the 30s through the 50s were great because television was non-existent or in its infancy at that time. Cartoons were made for movie houses and drive-ins (remember those?). They had to be well rendered to entertain people of all ages not just children. Cartoon quality dipped starting in the 60s because cartoons began being shown on TV as kiddie entertainment and kids don't care about the animation quality as the popularity of Ninja Turtles and Scooby-Doo attest. Why spend money making animation extravaganzas when the cheapest, crappiest shit will do as well with that particular demographic?
So everybody who says of these old cartoons, they don't make them this way any more, you couldn't be more right. The Fleischer Bros. studios could never outdo Disney though they tried but I enjoyed their cartoons every bit as much and thought they were further ahead in certain areas. I think the Fleischers invented rotoscoping which is where they film someone dancing and them draw a cartoon figure over the top on cels. When the cels are strung together, the cartoon figure appears to be dancing with amazing realness.
Another thing the Fleischers did was set up elaborate stage sets both in front of and behind the cels on top of a revolving table. The result is an amazing 3D effect as you will see here: