I've watched only the first episode of the new BBC production of Jamaica Inn so far and husband refused to watch the rest because it was too dull and depressing, so I've taped the other two episodes. So I can only comment on the first which has evidently proved highly disappointing to a great many people.
I do agree that the sound quality, or diction, was not good enough at times and the whole programme seemed a bit dark and muddy, while the women's costumes were not exactly true to the period. However, I'm aiming to watch the remainder as I still enjoy this type of story, although I've read a few complaints on Facebook that they give away part of the plot too soon - but I knew from the beginning what was actually going on.
Daphne du Maurier is one of my favourite authors and it's a good excuse to re-read the original story at some point. I love Rebecca and Frenchman's Creek and quite enjoyed the TV versions of the former. And for anyone who didn't already know this, she also wrote many short stories including The Birds and Don't Look Now, both of which were made into films.
Books made into films often cause controversy and the consensus is usually in favour of the original novel, rather than a visual adaptation. However, I can think of productions which I enjoyed as much as the novels, and in two cases I preferred the films. The famous BBC series of Pride and Prejudice, with Colin Firth and Jennifer Ehle, did full justice to the novel and characters and the Jane Eyre with Toby Stephens and Ruth Wilson was one of my favourite versions of that novel.
Two films which I preferred to the original book were The English Patient and The Horse Whisperer. The novel of the former was almost unrecognisable after I'd seen the wonderful film and less easy to follow, while the ending of the latter made much better sense than in the book. These are only my opinions, of course, but I'm sure some of you will have other examples of good and bad adaptations!