The lovely Choo loaned me Trouble Under Oz (2006) by Sherwood Smith, an authorized modern addition to L. Frank Baum's Oz series. The book is actually a sequel to Smith's first journey into the Oz world, The Emerald Wand of Oz, which I haven't read, but she gives enough background about the characters that, much like Baum's original series, you can read the books independently.
Dori and Em are two sisters in Kansas who have already had one exciting adventure together in Oz, thanks to a wild tornado. While they were there, Glinda gave them a special snow globe that they can use to see what is going on in Oz while they are back in Kansas. The two look at it all the time, and one day Dori sees Tik-Tok holding a sign that Glinda needs their help. Lucky for them, a series of unusual coincidences (snow storm, sick grandmother, fighting parents) clear the way for Dori to journey to Oz while Em stays home and covers for her. Once in Oz, Dori hooks up with Prince Inga of Pingaree (who you might remember from Rinkitink in Oz) to find Prince Rikiki, the son of the deposed leader of the Nomes who Dori met up with in her last adventure, and help him get his throne back while avoiding a war with the neighboring kingdoms. Oh and there is also some kind of trouble with Dorothy and weird black clouds, which is pretty obviously thrown in there to give Dori and Em something to do in the next addition to the series...
The three young people have some nice adventures with plenty of nods back to the original series. While the book is well written, it doesn't have the looseness or creativity of the Baum originals, but that isn't really Smith's fault since adding to a classic series is naturally a less free and creative medium than starting something from scratch. The book is illustrated by William Stout, who did a great job except that all his drawings show Dori with short hair and in one scene Em makes a point of saying that Dori's hair is very long -- am I a nerd for being bothered by this? I did like that Smith makes a point of having Dori ask where all the female Nomes are, since you never see or hear anything about them in the original Oz books, and the answer is excellent.
I'm not sure that this is a book that needs to be read by anyone except those who have a love for the Oz world, but if you do, then Smith's new additions to the series seem to be worth checking out.