This is the fourteenth Discworld novel, the third book to focus on Granny Weatherwax and the witches, and a direct sequel to Wyrd Sisters. That said, I remembered very little of Wyrd Sisters, which I read over ten years ago, and still found it generally comprehensible.
Lords and Ladies opens with Granny Weatherwax, Nanny Ogg, and Magrat Garlick returning home from the events of Witches Abroad. They are immediately plagued by a rash of crop circles, leaving Granny and Nanny quite concerned about the circle of standing stones called the Dancers. Worse, an upstart new coven has been dancing around the Dancers, risking the unleashing forces they don't understand. Magrat has other problems: Her very tentative possible future husband has decided that they're to be married on Midsummer's Eve without consulting her first, and she has to adjust to new and very unfamiliar life as royalty.
It becomes quickly apparent that the lords and ladies of the title, and the threat that Granny and Nanny are concerned about, are elves. These are not noble Tolkien elves, and are even less human and more sinister than the darker sort of fantasy. They are malevolent dimensional travelers who can break through when the walls between worlds are thin, something that is signaled by the sudden appearance of crop circles. As the story unfolds, it becomes clear that the kingdom of Lancre has been plagued by elves before, and that many of the local customs and traditions that now seem without purpose are defense mechanisms. But everyone other than Granny and Nanny have forgotten, and the elves have been offered a bridge back into Discworld.
I generally like Granny Weatherwax, but I think this is relatively minor Pratchett. Granny's normal insight and practical wisdom is transformed here to the anger of someone who remembers why things are dangerous and can't believe other people are playing around with them. That's less interesting, and more cliched, than her normal role. Nanny is obnoxious to her extended family, which Pratchett mostly plays for humor but which I didn't find funny. And Magrat spends most of the book bored and manipulated in ways that made it hard for me to either like her or find humor in her situation.
But the larger problem with Lords and Ladies is that it's a bit overstuffed. Granny and Nanny are pursuing one thread of the plot, Magrat is entangled in another involving castle life, Death shows up somewhat gratuitously, and even some of the wizards from the Unseen University get involved, rolling on the random encounter table as they come. I enjoyed seeing the Librarian again as much the next Discworld reader, but by the time Pratchett adds in the Morris dancers and some backstory revelations for Granny, it all feels like a bit much. The conclusion is a running multi-front battle that mostly involves characters struggling to get to the right locations, and which I found more confusing than choreographed.
As with Wyrd Sisters, Lords and Ladies is rife with Shakespeare references, particularly A Midsummer Night's Dream but also King Henry V and others. As with all of Discworld, see the Annotated Pratchett File to catch all of the references (but beware of spoilers). It's been a long time since I've read Shakespeare and I've never seen much performed, so most of this was lost on me.
Even weaker Pratchett is still fun, of course. There are lots of good jokes, some thoroughly enjoyable Librarian scenes, and a fair bit of Granny being a badass. I didn't find this take on elves particularly interesting, but the ending is entertaining and satisfying. I don't think this is the book that will sell someone on Discworld, but if you're reading through the series, no reason to skip this one.
Followed, in publication order, by Men at Arms. The later plot sequel is Maskerade.
As an aside, Discworld shows one of the serious drawbacks of the Kindle format and a dedicated reader. The reader does not handle footnotes well. The footnote itself is marked by a tiny underlined asterisk that is very easy to miss on the page or confuse for a quotation mark, and scanning each page for tiny footnote marks distracts from the reading. When I did see one, I then got to play the game of mashing my large finger on the screen four or five times until the Kindle finally realized I was trying to follow the footnote and not turn the page. It was a frustrating experience I mostly gave up on, meaning that I read all the footnotes at once at the end of the book. That's not the expected experience, and I'm now tempted to buy further Discworld books on paper. Or at least use the Kindle tablet app, which can use color to make footnote links slightly more apparent.