As regard to the acting styles, I totally agree, you have to accept it within its time. Modern acting, even Brando 1950s acting, wouldnt work in noir, or in 1930s performance styles.
With regard to history of film in general, I was slightly averse to watching films from like the 30s to the 60s, as most people who are young today are, until I wanted to learn more about film history and delved backwards. Now, I no longer have any problems, enjoy the acting, and can appreciate stylistic as well as acting differences fairly well. I just think its getting used to the movies again, which is what these marathons help do.