Those who have read Laurie King's series of Sherlock Holmes pastiches featuring Mary Russell know that Mary can easily be fitted into the category of "Mary Sue." But she's an interesting, well-rounded Mary Sue, whose personal Angst does not impinge terribly on her life after the first couple of books in the series, and whose eventual marriage to Sherlock Holmes is not portrayed in too much sickening detail. I can accept all this for purposes of pastiche. Holmes fanfiction does, after all, have a long and storied (heh) history.
King has also snuck the occasional cameo fictional character into her series as well. For example, an unnamed but clearly described Lord Peter Wimsey appears in a brief but vital role in one book. Her newest, The Game, uses characters from Kipling's Kim, one of my favorite books as a child and young adult, and still one of my favorites today (I reread it this year). I admit, I was nervous when I started The Game. I'm used to seeing interpretations of Holmes by people other than Doyle, but I've never seen anyone attempt Kimball O'Hara. King used a lot of dialect-spellings that Kipling uses, which annoyed me a little; I can see she did it to give the reader a flavor of Kipling, but in today's world having people say, "Oah, yes" all the time makes me a little uncomfortable, and there's no real reason I can think of to use a more formal English to represent people speaking Hindi.
The Game takes place in the early 1920s, so King alleviated some of my fears by having her Kim be 47 rather than 16 or 17, and by having him appear late in the book. Her extrapolations of his character were, I felt, reasonable. Yet I left the book faintly dissatisfied. I think it was because she had tried so hard not to impinge. I got only the faintest taste of what this adult Kim was like. I wanted to know how he'd become the man he was, and I wanted to see him be gloriously clever and sneaky and wear disguises. To see him be just another agent, albeit one who talks about Buddhism, was a letdown.
I don't think the book was bad. It just wasn't what I wanted.