Terry Pratchett’s I Shall Wear Midnight is the most recent in his “YA” Discworld series, featuring Tiffany Aching. Like the previous installments in this series, there’s nothing at all YA about it in any way whatsoever.
Also like previous installments in the series, it’s a pretty good book. The Witches subseries — which, really, the Tiffany Aching books are like Witches: The Next Generation — has always been one of the stronger lines running through Discworld, and I Shall Wear Midnight is in line with the other books in the series that way. It’s not a standout like Night Watch or Hogfather, but neither is it one of the weak books; it’s a solidly respectable installment.
And yeah, maybe Pratchett isn’t saying anything completely new here, but if you’re going into book 38 (or whatever) of a series expecting raw novelty, I don’t think it’s the book that has the problem. If you’re merely expecting the normal hallmarks of a Discworld novel — great characters, great writing, a deceptively complex plot, and a layer of social commentary — you won’t be disappointed.