When I read books I often try to visualize the scenes and expressions of particular characters, almost like I'm the director of a movie. There are a great many books I have read where I just could not justify them coming to the big screen. There'd have be too much monologue by characters for anything to make sense. A lot magical systems use inner thought to work. The readers could feel the struggle with them through description of the magic user's mind. Take Name of the Wind for an example, I think it would be absolutely impossible to implement it into some live-action ordeal. Every little action (through "magic" as Kvothe's world sees it) requires the reader's to grapple with abstract ideas for it to make sense. I'm not sure how a TV/Movie would explain that without a huge narration of some sort which then would turn that in to a read-a-loud. On the contrary I believe the Mistborn series would make a great TV/Movie. Its magic system is very physical. I can invision blue lines extending from the body connection to each metal source. I could see (through CGI and slo-mo) the amazingness of Atium. Have you any other magic systems that could be visually comprehended in their entirety?