Charlotte Bronte is not Jane Austen (can anyone talk about 19th century British literature, or women's literature, without at some point bringing up Jane Austen?- at least I can't). This can be both a bad thing and a good thing.
Bad: she is inferior as an artist. She lacks experience and doesn't have a sharp eye for character, and doesn't have Jane Austen's serenity and cool detachment- like Virginia Woolf has noted, Charlotte lets her indignation distort her art. More importantly, she's extremely bad with plot. Like Jane Eyre, the plot of Villette is contrived, full of implausibilities (there's no way one can read Villette without knowing that it's by the author of Jane Eyre). For instance, Lucy Snowe arrives in Villette, hoping to find Madame Beck, which doesn't seem easy because this is a city in a new country Lucy has never visited, and she doesn't know where the woman lives. However, whilst trying to find her trunk, Lucy meets and gets help from an Englishman, then asks him about an inn where she can stay for the night. He gives her the address of a place, which turns out to be Madame Beck's place. The man helping Lucy works there and is known as Dr John. A while later, during the holiday, Lucy gets sick, faints and is saved by Dr John, who turns out to be Graham, the son of Lucy's godmother in England, introduced in the 1st chapters.
Or, on a ship Lucy gets acquainted with a girl named Ginevra Fanshawe and, not knowing where to go, decides to come to Villette and find a job at Madame Beck's school, where Ginevra studies. Then it turns out that 1 of Ginevra's 2 suitors, codenamed Isidore, is John, aka Graham. Well that's OK. But later in the story, there's a scene when Graham and Lucy go to the theatre and he helps a girl, who is afterwards said to be Ginevra's cousin and who, as I guessed correctly, is later revealed to be Polly, the little girl who stays at Mrs Bretton with Graham and Lucy at the beginning of the story.
Such contrived, unnatural, unconvincing bits can be like little itches, seemingly insignificant but irritating nevertheless. Reading fiction, we know that everything's in the author's imagination, but still feel bothered when noticing the author's hand moving around in the story, touching this, moving that, instead of giving the illusion that everything happens naturally and follows their own course. Another detail is that, at the beginning of the story, the narrator doesn't speak French yet still can write down other characters' speech in French. The author clearly isn't very careful.
However, I shouldn't be unfair to Charlotte Bronte. It's a good thing too that she's not Jane Austen. She has the imagination, the power and intensity and boldness not found in Jane Austen (Charlotte's books are too exciting and imaginative to be read slowly). I've compared Jane Eyre and Fanny Price once- they are similar in many aspects, but Jane Eyre can do many things Fanny is never capable of. More importantly, in Charlotte, we find a yearning for something greater, a refusal to stay within bounds. She is never prosaic or mundane. She is poetic. Reading her books, one feels at one with nature. Reading her books, one is transferred to a different world. And she writes not to teach- Jane Austen never preaches, but still wants to teach or to make a point about virtue and balance, Charlotte Bronte doesn't do so. It's all about imagination and emotions. Not as cold and detached as Jane Austen, she is more personal and thus touches us deeply and moves us strongly.
And that is sometimes a lot more important than artistic perfection.