Here are some novels I’ve read recently, and my thoughts about how easily they could be adapted to screenplays.
Cat Out of Hell, Lynne Truss — There is quite a bit of action that is directly adaptable. The novel is presented as a mish-mash of formats, including interview transcripts, emails, and descriptions of photographs. All of that would need to be discarded, but that would create some challenges about how to unfold the story. I don’t envy the filmmaker who must direct a considerable amount of action involving cats, let alone talking cats, but that’s really not the writer’s problem.
Spock’s World, Diane Duane — The main story would quite easily adaptable to film, and by itself it would undoubtedly be an appropriate length for a feature film. However, the novel also includes a series of vignettes that contribute to world-building of Vulcan. Each of them ought to be reasonably adaptable, but I’m sure the final product would be a film that is too long. One could simply omit the vignettes and have a solid story, except that the story depends somewhat on the vignettes for mood and a little background. While the vignettes would increase the total production cost considerably, enriching the film cannon of Vulcan would have more value to Trek fans than would one more otherwise mediocre Star Trek story. Who would produce such a film? With Leonard Nimoy and DeForest Kelley dead and William Shatner in his late eighties, the could only be done in the J. J. Abrams reboot series, but this story doesn’t have the requisite amount of action to fit. Could it? This could only be a writing exercise.
The Left Hand of Darkness, Ursula K. Le Guin — There is much said in this novel about gender and gender roles, and I’m afraid much of it would be lost. Furthermore, the central invention of the story is the concept of a humanoid species that is neither and both male and female, but could you show that in film? In the book, it is described, but no actual sex takes place in the story. Furthermore, even if there were the opportunity, how could you possibly show what needed to be shown? It would be a weird kind of pornography. Therefore, you simply cannot show it, and the writer must figure out another way to get the point across. Today’s appetite for media about gender issues is quite large, but could you do the story justice in those ways? All of the feminist observations are Genly Ai’s private thoughts.
The Raven Tower, Ann Leckie — The obvious challenge here is how to tell a story from the point of view of a rock. Actually, a good portion of the story takes place in a fairly normal way. Sooner or later however, the rock needs to be brought into it. A talking rock. I’ll have to think on that.
The Cloud Roads, Martha Wells — Adapting this story to film would be fairly straightforward. Of course, the film would require a significant amount of CG, but that’s not the writer’s problem.