1 big difference was the actions of these/those stars off screen. There were several actors who left that lively hood to enter the Armed Forces, that just doesn't happen today. The idea of glamour IMO was much different as well, the decorum of the actors was almost 180 from today as well.
As far as the acting goes so much of todays films IMO delve into so much special effects is that to add to the movie or hide acting flaws? Also it looks to me that ideas for movies are more of a "steal" from an old movie. Now keep in mind I really don't watch newer movies and keep to the "oldies". There are good actors today, but IMO the footstep they leave behind is not as prominent as the old stars.....The glamor, the mystery, the "coolness"......it's just not there, to me it doesn't exist.