Terry Pratchett's 4th Tiffany Aching book, "I shall wear midnight" is really good. I loved reading it and I look forward to reading it again soon.
My only quibble is with the target audience. I know Tiff is growing up, and perhaps the idea is that the readers grow up with her, but as she's sixteen, I expect 12-14 year-olds to want to read the book, particularly if they'd read the previous offerings in the series.
Now I know some 13-year olds have sex. I know most of them use swear words. And yet I don't think it's appropriate to include swear words or teen pregnancies in a Discworld book.
Oh dear, now I sound like my own father, LOL. And, to be fair, my mother let me read "Rich Man, Poor Man", with all its sex scenes and violence when I was 12, and I didn't get corrupted by it. So who am I to argue?
Still. There are lots of teen books out there that deal with sex, drugs, bereavement, divorce and family violence. If teens need them, it's important that they exist and are accessible.
It's just that I would have preferred Discworld books to remain pure fantasy and escapism from the world tainted bleak by teen hormones...