I love Jamaica Inn, I've read the book countless times, got the Hitchcock version, watched an early 80's series with Mary Crosby as Mary Yellan, I've also been to the real Jamaica Inn, which was a dream come true for me,
I loved this, I heard it fine, and at last a drama set in the early 19th Century that shows real grime, and what Jamaica Inn must have looked like then.
Agree that they have changed some details, the book is set before 1821, and I'm sure Mary doesn't meet Jem Merlyn til later in the book.
Also not sure about Aunt Patience and Joss Merlyn,
In the book, Patience has grey tattered hair and wears a very faded pink gown, and Joss is a bear of a man, though their characters were well portrayed.