My favorite period of animation was from the 30s to the 50s. That's when the most creative and skilled cartoons were made.
Things changed quite a bit during those 30 years and in a general direction. I picked out a handful of cartoons that typify each period. They follow the major trends of the times.
(I left out New York cartoons for the time being, because for a while Fleischer defied the trends and went its own way.)
These are all west coast cartoons, done by the same basic groups of people using all the same principles only in different proportions and with different focuses.
Late 30s - Building the toolsThings changed quite a bit during those 30 years and in a general direction. I picked out a handful of cartoons that typify each period. They follow the major trends of the times.
(I left out New York cartoons for the time being, because for a while Fleischer defied the trends and went its own way.)
These are all west coast cartoons, done by the same basic groups of people using all the same principles only in different proportions and with different focuses.

(I don't know who did these scenes)




Acting:
http://www.cartoonthrills.org/blog//Dis/magmick37/mickDonsml.mov
Magician Mickey 1937










But only possible if you have the imagination and the permission to use it.
40s - Applying the tools to creativity
Action ending with acting:
http://www.cartoonthrills.org/blog/Clampett/Cuff/spiderruntalk.mov
The Warner's directors had less money to spend on their cartoons than Disney and maybe that helped force them to have more restraint and control over their animation. Every action and every part of an action could not be equal.

Clampett focused the techniques around crazy stories, great acting, a richer assortment and variety of gags and swinging music (unlike the softer whitebread Disney scores). He gave all this new animation punctuation, but punctuation wrapped around the ideas, not just random punctuation.
Avery, Tashlin and Clampett also took the cartoons away from the juvenile Disney arena and aged them up to merely immature.

These cartoons are much more human-friendly and that's part of why they have outlasted Disney's and are still very popular with all ages today.
More than anyone else, Clampett really upgraded the acting in cartoons. His characters have a much wider and more specific range of expressions than the Disney stable of characters.

For me, having strong characters who really portray human traits and foibles makes the magic and insanity of cartoons even more fantastic. It's like it's real and impossible at the same time. It's better than real.

Action ending with acting:
http://www.cartoonthrills.org/blog/Clampett/Cuff/beefightsmall.mov

Clampett's wild action is not merely wild. It's focused. This scene of the butt battle is hilarious and super fast. It's incredible that you can tell what's happening. The faces and torsos move less than the wildly flailing buttocks and that makes us focus in on the asses.


The Warner's directors, especially Clampett, allowed their animators more stylistic individuality. Here Scribner animates with an approach that I've never seen anyone else do. If you slow frame through the clip try to follow how one drawing animates into the next.

50s - Hiding the tools
Acting:
http://www.cartoonthrills.org/blog/Jones/bonnets/01BugsElmerArmyDialsmall.mov
There are at least 2 theories as to why the Warner's cartoons went in this direction. The history books explain that the budgets were cut. The directors themselves say they like these cartoons better than their 40s cartoons, so this less animated style is partly by choice.
This animation is expert and could only be done by artists who had learned the 30s and 40 principles. All through Chuck Jones' later cartoons, there are moments of fun animation, but it's usually squeezed in between Jones' own poses.
Action:
http://www.cartoonthrills.org/blog/Jones/bonnets/02bonnetsactionsmall.mov

50s cartoons are more controlled than 30s cartoons and even more controlled than 40s cartoons, but it's a kind of repressive control that to me, really undermines the potential of animation.

A chase scene like this would have been animated with humor and noticeable invention in 1942. Here it's animated almost to hide the fact that it's animated. It's perfectly smooth and clever, but to an audience it's merely running and shooting.


The drawings in this and other 50s (esp. Jones) cartoons are also expert. They have tricky and clever structures, are organic, have a variety in the shapes and forms and are extremely carefully controlled. Yet they don't say anything noticeable. It's just enough cleverness to make the story point, but not much more. There is no joy of the magic of animation. No extreme pleasure of performance.



So far, all these cartoons use the same basket of skills and principles, but apply them in different proportions and to different purposes. You had to be highly skilled and talented to do any of these styles.
Now here's a style that you don't have to know anything to be able to do.
50 more years of progress
Action or Acting?
Action ending with acting:
http://www.cartoonthrills.org/blog/Clampett/Cuff/spiderruntalk.mov
It took Warner Bros. cartoons to find controlled ways to apply the new animation techniques. They combined early cartoon humor and magic with animation principles and their own advances in timing. On top of all that, they added something brand new - the idea of a personal point of view. And the audiences went nuts.


Clampett focused the techniques around crazy stories, great acting, a richer assortment and variety of gags and swinging music (unlike the softer whitebread Disney scores). He gave all this new animation punctuation, but punctuation wrapped around the ideas, not just random punctuation.


These cartoons are much more human-friendly and that's part of why they have outlasted Disney's and are still very popular with all ages today.


For me, having strong characters who really portray human traits and foibles makes the magic and insanity of cartoons even more fantastic. It's like it's real and impossible at the same time. It's better than real.

Action ending with acting:
http://www.cartoonthrills.org/blog/Clampett/Cuff/beefightsmall.mov

Clampett's wild action is not merely wild. It's focused. This scene of the butt battle is hilarious and super fast. It's incredible that you can tell what's happening. The faces and torsos move less than the wildly flailing buttocks and that makes us focus in on the asses.


The Warner's directors, especially Clampett, allowed their animators more stylistic individuality. Here Scribner animates with an approach that I've never seen anyone else do. If you slow frame through the clip try to follow how one drawing animates into the next.

50s - Hiding the tools
Acting:
http://www.cartoonthrills.org/blog/Jones/bonnets/01BugsElmerArmyDialsmall.mov
By the 50s, all the animators that had at one time done lively bouncy animation were now slowly abandoning it in favor of walking talking cartoons. Characters would walk from one scene to the next, say their lines, react and then go on to the next. Jones called it "Illustrated Radio" and he did it best.


Action:
http://www.cartoonthrills.org/blog/Jones/bonnets/02bonnetsactionsmall.mov

50s cartoons are more controlled than 30s cartoons and even more controlled than 40s cartoons, but it's a kind of repressive control that to me, really undermines the potential of animation.

A chase scene like this would have been animated with humor and noticeable invention in 1942. Here it's animated almost to hide the fact that it's animated. It's perfectly smooth and clever, but to an audience it's merely running and shooting.


The drawings in this and other 50s (esp. Jones) cartoons are also expert. They have tricky and clever structures, are organic, have a variety in the shapes and forms and are extremely carefully controlled. Yet they don't say anything noticeable. It's just enough cleverness to make the story point, but not much more. There is no joy of the magic of animation. No extreme pleasure of performance.



So far, all these cartoons use the same basket of skills and principles, but apply them in different proportions and to different purposes. You had to be highly skilled and talented to do any of these styles.
Now here's a style that you don't have to know anything to be able to do.
Action or Acting?
A few commenters observed the same things I just wrote about. Noteably Amir, Ardy and Roberto. Good eyes, fellas!
Oh and Will Finn just posted an in-depth analysis. Thanks Will!