And so, in 2005, The Seven Blue Mountains of Oz trilogy was finally completed. Melody Grandy, for reasons of her own, had left it rather unfinished, so a few writers who'd written for Tails of the Cowardly Lion and Friends took silent credit and polished it off for publication. Melody did do a final edit, though. The handful of her completed illustrations were supplemented with new art by Luciano Vecchio and Marcus Mebes.
Now that Zim is known throughout Oz, he has some things to take care of as Wizard of Munchkinland. First off is helping Orlando recover his mother and step-father from Herku, then settle the giants of Huge Mountain as Orlando takes leadership of them.
Also, Thorns and Private Files of Oz gets its wrap up with a twist you didn't see coming, and neither did Zim, which gives a new perspective to his character.
Later, Zim attempts an experiment, but ends up putting a lot of trouble into the Wizard of Oz's hands: he splits into 31 pint-sized versions of himself, each a personification of one of Zim's traits, some he's kept subdued, including Love and Cruelty. While this might seem like a cartoon plot, it's a lot of fun to read, especially considering the trouble the Wizard and the Emerald City folk have containing Zim's traits, much less finding a way to get him put back together!
But get back together Zim does (though I'm not telling you how, you'd figure out that happens just by looking at the table of contents) and resumes his duties. He investigates a giant who makes people play a board game called the Battle of Kipo until they win.
Zim and Tippetarius visit Zim's great-grandmother in Tir Na n'Og, where Zim must defeat the Black Druid, who has been terrorizing the faeries who live there. And then, Zim finally answers summons from Tititi-Hoochoo, the Great Jinjin.
And also a couple final loose ends of the trilogy are tied up, but I'm not saying how. You should really just read these for yourself.
While Zim Greenleaf of Oz answers many questions, that turns out to be its major weakness: an answer is never as interesting as a question. However, since we were following these questions for two or three books (if you count Thorns and Private Files in Oz), we do want to see these answered, so it makes for a good read.
The illustrations vary quite a bit in style, all being wonderful in their own respects, but as the designs of the characters stay the same, it doesn't disorient the reader.
So, yes, if you've read the other two books (and Thorns and Private Files), by all means, pick up Zim Greenleaf of Oz.