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From Beyond does prove a Lovecraftian adaptation that isn't embarrassing is possible.
I am currently reading a book that, I'm not sure if it was ever adapted, but is impossible to imagine could ever do justice. James Agee's "Let Us Know Praise Famous Men" is so dense in its prose, and attention to the detail of this man's experience in the South, I feel all the sublety would be drained from it if it were put on screen. So far the actual action is fairly standard, but it really sparkles because of the inner conflict the author is having in using these people to create a piece of fiction. It's astonishing and would likely lead to a very mediocre book.
Also, I've never dared go near the Jonathan Strange and Mr Norrell mini series because it is the rare example of a story that I think I really need all of the subplots to be considered on screen. And there are just so many of them, I haven't bothered with the adaptation (which was apparently shit anyways)