I have just started in on Mansfield Park, reading my Collins Classics paper copy for old times' sake! The introduction in that includes a quote by Sheila Kaye-Smith suggesting that the "shadow" which has fallen over MP and which is not over the earlier three novels could be linked to the Evangelical Revival. I don't know anything about this and am going off to look it up. It is certainly a darker book, even from the first chapter, as you say fantasyfan. But there is still room for a delicious Austen crack at social attitudes on the first page:
"But Miss Frances married, in the common phrase, to disoblige her family, and by fixing on a lieutenant of marines without education, fortune, or connections, did it very thoroughly."
And no wonder poor little Fanny was so timid and shy given the attitude of Aunt Norris who encouraged the Bertram girls to look down on her as inferior.