There are so many fantastic things about Mr. Nobody that I would definitely recommend it, but there are also many annoying things that could turn someone off. So here is my endorsement, with caveats.
See it: The story jumps all over time and parallel existences. We (try to) follow the protagonist, Nemo, as he lives different lives as himself. It’s not chronological, so sometimes it takes a moment to orient yourself in the storyline. Despite the potential for confusion, the multiverse is actually one of the strong points of the film, if you let yourself be carried along by the stories. You can believe that Nemo could live all these versions of his life, and you can sympathize with each of his selves. The film is long, and necessarily so, in order to develop a character over a lifetime for several different existences. I watched it over three sittings, and I was instantly absorbed by the story each time. Nemo is excellently acted by three actors at different ages, and they all believably portray the same person, so kudos to the casting director! Another strong point is the stylized cinematography; it’s beautiful to watch.
Caveats: One of the weaknesses of the film is the lack of development of the present-day setting, where Nemo is looking back on his lives and telling his story. I could hardly stand to watch these scenes because they did too good a job of making the future plastic and obnoxious (a microphone face-implant? Gross!). Also, despite some stellar special effects and makeup in the film, the dying Nemo is hokey-looking to the point of distraction. And the final warning is that the story is heavy on sentimentality. At first, I was distracted by this, but if you can get past the sometimes overwrought style, you can invest in Nemo’s stories.