There are two serious flaws that run throughout a majority of the story. While the steam castle is an amazing and serious piece of technology run by the sinister O'Hara Foundation, it is completely baffling why the leader allows his young daughter to run free throughout the complex like she is Eloise at the Plaza Hotel. These men are trying to conduct experiments and business that are serious, and at times dangerous. They don't need a bratty girl getting in the way other than to have a damsel in distress for Ray to rescue. She was unbearable in every scene she was in, which is too bad, considering she's the female with the biggest role in the story. And would someone explain to me why so many young girls in anime have shrill, annoying voices.
The other problem is how quickly Ray took to learning to fly. I know he's supposed to be an inventor as well, but there's no evidence that he has a background in aviation. If he had been in a plane or something similar, I could have suspended disbelief, but he rides a steam ball, a small orb that he attaches handles to, embracing it with his body. He whizzes around at amazing speeds, never seeming in control of the device, yet always able to get where he needs to. If it had been in short spurts, it could have worked, but to seem him navigate through the tunnels of the steam castle was too much.
The greatest disappointment is the waste of such gorgeous animation. The drawings looked great and had amazing detail. You should rent the film and then fast forward through it, pausing occasionally to appreciate the beauty and skill required in creating it. There should be a book entitled The Art of Steamboy, which I would recommend; however, the film I cannot. If they went back and cut down the last hour, it could work, but I don't see that happening.