As a child in the 1930s I thought Paul Muni one of Hollywood's best, but I can't recall the movies on which this judgment was based. I don't know whether I saw this film then or not.
Now I find the depiction of "great writer (Zola) and great painter (Cezanne) in Paris during the 1800s" to be a grade school or Sunday school version of life. Hollywood's description of the Dreyfus affair lacks complexity, sophistication, reality, accuracy. The true story abounds in dramatic interest, excitement, conflict and power quite beyond the movie's reach.
But we do have two marvelous speeches, one when Muni as Emile Zola is reading his pamphlet, "I Accuse," to his friends and allies. And the other, when he is defending himself on a charge of slander in a hostile court. These alone are worth more than the price of admission. Spend your time hearing them again and again and then get yourself a copy of Zola's pamphlet and a good book from Amazon.com on what the Dreyfus affair was all about.