The original film is a masterpiece of course. It's hard to imagine a better (or equal) "Mrs. Danvers" to Judith Anderson, although I would expect Diana Rigg would have done the role justice, too (speaking of a BBC version I saw too long ago to remember very well).
I was really looking forward to last year's film of "My Cousin Rachel" after reading the excellent novel by DuMaurier, and the trailers looked very good. The more I read about that version, though, the less I wanted to see it, and never did. I learned about the book from catching the last 15 minutes or so of the Richard Burton-Olivia de Havilland film version which caught my interest, though I never watched the DVD after purchasing it a few years back.
I've never actually read "Rebecca," but I've heard that it is jarring and troubling by the end as far as the characters of Maxim and his wife, as is the case with "My Cousin Rachel."
