The following is just my opinion, and nothing more-only opinion. I don't work for any movie people and I'm no academic or be all end all authority. This is only what I've observed. 1930's movies-came in two flavors: A) Well contructed dramas that came from plays, books, or well constructed screenplays. Actors involved in these projects were selected by the director and followed the script carefully. Their continued employment depended on this fact. B) A series of musical numbers, accented by dancing, loosely linked with a thin plot which linked the numbers together. Entertainers involved in these movies were vaudeville trained and excelled at acting, singing, and dancing. 1940's movies C) Add in military movies, which under the careful hand of patriots, lauded the Americans and made villains out of the enemy. 1950's movies A) Add in a new type of movie which questioned societal values. A good example would be Twelve Angry Men. B) Inspired by the space race and red scare, there was a series of, mostly bad, sci fi movies. An example of a bad one would be The Wizard of Mars. An example of a good one would be The Day The Earth Stood Still. C) Westerns were cheap and easy to make and were made in the hundreds. 1960's movies A) In the mid 60's, musicals died. Sound of Music was an astounding success and 1968's Oliver was a blip on the radar, but very much death after that. B) Dramas gave way to hippie movies (i.e. Five Easy Pieces, Easy Rider) which folded in the societal questioning movies (Dirty Harry). C) War movies were at their very best in the 60's. The Longest Day, Tora, Tora, Tora, The Green Berets and The Alamo are great examples. It's a pity that the end of the 60's saw the beginning a long slow descent. D) Nudity moved from the shadows into the mainstream. Actresses now made nude scenes, the first mainstream nudity since before the self imposed Hollywood code imposed in 1934. 1970's A) We are fortunate that Italian film makers cast Clint Eastwood in a series of spaghetti westerns. These movies have become classics. John Wayne, owning his own Batjac Productions, started a series of well made westerns in the 1960's which endured all through the 70's. B) The mid 70's saw a new type of movie, which was the infancy of the blockbuster era. Jaws was the first blockbuster, followed late the next year with the surprise hit Star Wars (episode IV) 1980's A) The blockbuster era took off. George Lucas made Star Wars sequels and started the Indiana Jones franchise. Spielberg had a gargantuan hit with E.T., which eventually led to a series of pretenders. B) Nudity really peaked with the new teen comedy genre. Fast Times at Ridgemont High was a hilarious, but very factual look at life in and out of an American High School. In the early seventies, nude scenes lasted anywhere from five to ten minutes in length, but were poorly filmed. Early 80's nude scenes were plentiful,mandatory in many movies, about a minute in length, but were excellently filmed. 1990, saw a self imposed ten second nude scene rule. Also, nude scenes severely diminished in quantity and quality. 1990's A) Movies suddenly became gritty, graphic, and downright depressing. Movies became made when actors picked their projects, and scripts. Scripts were often dumbed down to fit the laziness of the actor. Actors prefer to play flawed people and the consumer was subjected to a cram down the throat process. Unfortunately, people bought into this. B) Blockbusters pretty much became the rule of the movie making process as the average price of making many movies hit 100 million. George Lucas invented CGI and many movies depended on the studios owned by Lucas creating the effects used in movies. 21st Century A) Movies became a series of stunts and eye popping effects linked by a loose or thin plot.