Dylan's not there--he doesn't appear in the movie (well, except for a small clip at the end, as a shadow of himself, almost). A series of actors who "weren't there" play him, a series of substitutions. The movie reproduces and quotes numerous other movies from other Dylan documentaries to Fellini's 8 1/2, and in a way, referencing these highlights the fact that we weren't there. A reference is an acknowledgement of existence, of knowledge, but also an acknowledgement of absence.
You start to realize that the actors playing him aren't all trying to act like him. Exact replication isn't the goal here (except for Cate Blanchett who does an excellent job). When you have a black boy play Dylan, it makes relating to him as Dylan, as "there", that much harder, and that is part of the point of the film. Richard Gere doesn't even TRY! He acts exactly like Richard Gere in all his other shitty movies. But it's this quality that makes the movie unique and much more interesting than other biopics.
It shuffles between reference points as well as styles. A black and white scene reminiscent of 8 1/2 is followed by an interview with Julianne Moore in full color, reminiscent of a mockumentary. Though the film is so restlessly shuffling, it manages, amazingly, to capture something about Dylan. The nonconventional storytelling style really benefits here in being enigmatic and revealing at the same time. Who is this person? We are asked to do the other half of the work, to place ourselves there in our minds.
It's not without fault. The performances were spotty. Some were amazing, like Cate Blanchett who was really great at her role about 90% of the time, Charlotte Gainsbourg, who gave a real standout performance here, even though she didn't really do anything that spectacular. She was just very convincing and lovable and real. There were bad performances too, Richard Gere was awful, the black boy was good when he was playing the charismatic Dylan, but he was awful when he tried to act meditative, David Cross as Allen Ginsberg was so much of a joke that it was hard to judge how well he played the role. But in a way it doesn't really matter, the format of the film absorbs the bad performances because the film itself draws attention to the fact that none of this is real, you're constantly aware of the fact that this is acting, and that's part of the point. It's almost like an exercise, but one in which there is a little bit of heart, which is what redeems it. The incredibly generous heart of Dylan, or part of it at least, comes through all the noise and makes the film that much more convincing. He's hiding in the film, even though he's not there.