While there have been several comic books(series or otherwise)based on Oz, there have only a few direct graphic novels of it. Usually, a graphic novel is either a book collecting either a comic mini-series or a volume of an ongoing series, while other times it is an original publishig made specifically for that print.
Penguin Group recently printed a manga-styled version of The Wizard Of Oz, adapted and drawn by Michael Cavallarao whose worked on DC Comics, Valiant, and Cartoon Network. Not much is different from the original story, aside from the fact it more or less has been moved to the 21st Century. Dorothy seems more like a young teenager than around ten years old, plus Tin Man is very much modeled after the Iron Giant.
There's some pretty good designs and artwork in it, even though it might seem not up to specs of that from Oz: The Manga. It's a very good pick for younger readers, or for parents who want their kids to be comic nerds.