I haven't read the book by Robert Penn Warren, and I haven't seen the 1949 film, which is supposed to be great. I found this movie interesting and well-acted, although the only actor to keep up his Southern accent was Sean Penn.
But what's really interesting is the Louisiana politician the book and movies are based on, Huey Long. I didn't know anything about him before--he sounds like a pretty fascinating guy, probably more so than Willie Stark, the fictional character inspired by him.
Also of interest was the Louisiana State Capitol, where the movie was filmed. Huey Long had the capitol built from 1930–1932; it's the tallest capitol building in the United States, and it's pretty weird-looking.