Things turn out well for Becky Sharp at the end of this Vanity Fair. Surprise! It's not like the novel. But is there anyone who's ever read the book who didn't want a better fate for Becky? I imagine Thackeray reading through the book one last time before final revisions, saying, "Gosh, I wish my sense of morality and overall plan for the book allowed me to give her a husband and just a small fortune." So what Mira Nair has done is understandable.
It's not Thackeray's Vanity Fair, but that may be OK.
There are a few other changes as well. George Osborne is a more thoroughgoing villain: It's Osborne that keeps Becky from marrying Jos Sedley at the beginning, not Sedley's own shyness. Osborne says he won't marry into a family to have Becky Sharp as a sister-in-law, giving Sedley choice of sacrificing his own or his sister's happiness. This nicely sets up the ending. (Think Persuasion more than Vanity Fair.) Dobbin has a tendency toward priggishness in the book, but here it's turned up several degrees, so much so that I wondered when Amelia finally does marry him at the end of the movie if she's made a second bad choice. But then was there anyone who didn't think Thackeray's Amelia was weak and undeserving anyway?
So, I thought it was a pretty good movie on its own terms. Were there any flaws? Two, one that I'm sure of, and one I rather suspect. First, the film does follow the book closely enough that Thackeray's logic really should apply. Becky's grasping is not entirely charming. She's always ready to give up the bird in her hand for the two in the bush. The Marquess of Steyn (more worldly wise and bemused than in the book) tells her as much, that none of it will make her happy. Has she learned and will she be content with her marriage and small fortune? There will be no more dancing for the King. If she's learned anything from her adventures, we don't see it, and I'm not sure her implied future happiness makes sense or is earned.
But I also wonder if the movie's intelligible. I read the book, some years ago now, but I have read it. Does any of it make sense if you haven't? I can't comment on that, but I do wonder.