It's setting, with a mashup of 18th century sailing ships and futuristic space travel, does not hold much in the way of believability, but certainly captured my imagination. I've always been a fan of "airships," and this movie certainly provides an interesting take on the idea. I also liked how the technology was a mixture of science fiction and the mundane.
In the end, it's the characters that draw me in. I immediately adore the protagonist's mother and wish that should could have been a larger part of the story. Every character seems to have a deeper story beneath what we get to see in the film. The greatest element, by far, is the developing relationship between young Jim and the cyborg, John Silver. This film really emphasizes the importance of having an interested role-model in a young person's life.
There are plenty of reasons why it isn't a great movie by most people's standards, but it's one that I can watch again and again. That's the most important standard in my judgement.