A book that helped me understand what's going on in Austen the best was titled "Jane Austen and the Fiction of Her Time". Jane Austen loved novels, but was also dissatisfied with what she saw as the flaws of a lot of the novels around her -- both in the plots (unrealistic situations or unrealistic characters), and with the message they were trying to present. So many of the situations are direct allusions to other novels, and many of the main messages are subtle and subversive.
One of the things pointed out about Mansfield Park is that although all ends well for the main characters, it's basically by accident. If Henry Crawford had just gone back to check on his steward, as he knew he should have, he never would have been snubbed by Julia; would never have been tempted by wounded vanity to win her back; would never have run off with her, putting himself completely out of Fanny's reach; and would, in the author's estimation, have won her over eventually. And if Henry hadn't run off with Julia, Mary would never have exposed her lack of principles to Edmund, and they would have been married shortly too.
the most complex of the Austen rakes, destined to be "the nearest-run thing you ever saw in your life", according to another regency quip, HC was
I don't see that quip in that link? It seems to think that Mr. Elliot is the most dangerous of rakes, and I'm inclined to agree.
But there's an unexamined assumption in that piece that good characters should be rewarded and bad characters punished by the author. That's exactly the sort of thing that Austen hated. She wanted things to be things like real life, where adultery and cheating and lying and defying the law can bring you hundreds of millions of loyal followers and a second presidency.
Why was Henry not punished like Julia was? Because he owned land and she didn't. That's the beginning and end of it. It's unfair because society is unfair.
And it's not just men who get away with things. Lucy Steele lies and schemes and manipulates her way all the way through Sense and Sensibility, and is rewarded by being not only an heiress of a great fortune, but a favored daughter-in-law. The difference between Lucy and Julia aren't their morals -- Lucy is far less moral than Julia. She's just a lot smarter and more disciplined.
Ah.. realism you say? Elliott was not nearly as attractive (=less of a danger, even in the mind of the author, I venture-- its not a coincidence he is related to Anne! )
Otoh HC was (apparently) as reformable as a boy can get without actually being good = seductive
(Should have made clear that it's from Wellington, an admirer of Napoleon https://www.quora.com/What-is-the-meaning-of-Wellingtons-quo...)
Aha! Mansfield Park has been my favourite, since the 1980s. Most Austen fans seem to dislike it, and see the central character as weak and insipid. But, I see it as about code switching and timidity, she's clearly an introvert being bullied by the family.
The intrusion of Caribbean wealth is slavery. Edmond should be more overtly concerned about his families wealth, although to be fair it was mainly dissenters who did this, not the recipients of a family living.
She's on the money for naval preferment. Without help, commoner middies didn't make the crucial step up towards post captain. And for preferment, sexual favours by a sister would be common.
It may be important to note that all of Austen's novels are set up and kept going by an essential flaw in the hero characters. And Fanny Price is the ultimate anti-hero: indeed, she is hardly a heroine, she doesn't act, at all, she has no arc, she just clings to the first thing she encounters. While the world is moving and swirling around her, she doesn't move at all, not for lack of opportunity, but as a character trait (and, at times, by sheer luck, as in the theatre episode, thus earning her uncle's regard). And, in the end, it's all for nothing: while she got everything, she may have wanted to embrace, and even more, she is untouched by it and (quite literally) still where she started. It's quite literally about first attachments, not just in the domain of romance (like in Sense and Sensibility), but to about everything. Or, rather, first possessions, as in the first room, she may call her own, the first person, she talks to, etc.
How Austen constructs a plausible environment for such a character and what she does with this world and its characters is quite astounding – and hilarious. And, as you said, there are actually serious topics discussed.
Even more astounding is maybe how modern adaptations try to render this as "how our quick and cunning girl stirs up that lame family and wins everything."
PS: As a literary stunt and challenge, the question, how can we do an entertaining and involving novel with an entirely inert heroine and protagonist?, isn't that dissimilar from Umberto Eco's chosen challenge, how can we do a who-done-it where the book is the murderer? (as seen in the Name of the Rose.) And Jane Austen masters the seemingly impossible quite impressively.
Mrs Norris is also superbly well personified. She knows the worth of a roll of green baize. Her life and livelihood depends on it.
It's probably the best thing after the well-meaning social execution of Jane Fairfax, Emma's foil, by Emma's father for the exceptionally dangerous luck of having wet socks.