He wrote a lot of movie criticism -- some for the Nation, some for....I forget. Here's his piece on "Best Years of Our Lives" in the Nation.
http://www.thenation.com/article/best-years-our-lives#
I think he is entirely fair to the film; he liked it quite a bit. Modern Library has collected all his essays on film in a book titled "Agee on Film." Great good stuff on Chaplin, silent comedy, and John Houston whom he rightfully loved, especially "Treasure of Sierra Madre."
Joanna