For any fan of the Marx brothers' films in general and A Night at the Opera in particular, Remarks on Marx is an entertaining documentary, in which writers, actors and other Marx enthusiasts from the film industry talk about different aspects of the films. Divided into several topics, it covers the creation of the brothers' personas and their career (from the early films with Paramount to the subsequent success at MGM, their vaudeville tours and their relationship with Irving Thalberg), as well as some classic sketches such as the stateroom and contract (i.e. sanity clause) scene.
However, while there are some amusing anecdotes that might not be available elsewhere, anyone looking for a nuanced or particularly incisive film about the works of Marx has come to the wrong place, as most of its entertainment derives from hearing film enthusiasts talk about why they love the franchise. But while it will probably not add to my enjoyment of the films, it will not take away anything either, as might have been the case if the documentary had gone too far down the route of explaining why we are laughing.