Based on the book Dorothy of Oz by Roger Stanton Baum, that was also its working title. I can only figure they changed it in hopes of launching a franchise, but since the film isn't doing all that well at the box office this probably won't happen. I have to wonder if a sequel would adapt another Roger Baum book or something totally different.
In general, I think Roger's books get more attention than others simply because he's L. Frank Baum's great-grandson, even though there are much better authors writing unofficial Oz sequels. Melody Grandy's Seven Blue Mountains of Oz trilogy, for instance, would likely have made a much better movie. Still, I think the creators had a much better grasp on Oz than did those for Oz the Great and Powerful, particularly when it came to the humor.
It got off to a rocky start due to some weird decisions. Why, for instance, were the Kansas parts set in the modern day? And why did the people look like characters from The Sims? Once it got into more surreal landscapes, it worked better, something I've often thought about computer-animated films. Besides, I realize it didn't have the budget of big studios, and I would imagine most of the money they did have was spent on the voice cast. There were songs, but none of them were at all memorable, at least to me.
As an adaptation of the book, it was pretty loose, using characters and situations in quite different ways than those in which Roger wrote them. The Candy Country with a marshmallow person as a prominent resident, Wiser the Owl, the China Princess, the talking boat Tugg, and an evil jester who had harnessed the power of the Wicked Witch of the West all appeared in Dorothy; but were altered for the film in ways, usually in ways that were at least supposed to make them more comical. Dorothy in the book does encounter Wiser outside the Candy Country with his body covered in molasses, but his being overweight was new, as was his habit of talking incessantly.
And while the original Jester was a hapless individual who had been corrupted by the Wicked Witch's wand, the film made him the Witch's brother and more irredeemably nasty. His over-the-top persona made him a more interesting and entertaining character than he was in the book, as well as a more believable threat. The China Princess was pretty true to character, and while her romance with Marshall Mallow seemed a bit tacked on, it worked all right. It did seem like her size wasn't always consistent, though. There wasn't much to the plot, and the defeat of the Jester essentially just came down to all the other characters in the movie distracting him while Dorothy took and broke his scepter. Still, despite its flaws, it was mostly a fun experience.
As might be expected, there were several nods to MGM. I recall seeing early descriptions of the movie that blatantly incorporated elements like the farmhands from the famous film, but the creators apparently got into legal trouble and had to tone down this kind of thing. Still, there were characters in Kansas who had counterparts in Oz, and a specific reference to the apple trees in the 1939 movie. The familiar characters were often about as close as they could get to MGM without legal issues. Glinda in Legends wore an outfit like Billie Burke, but her bright red hair was likely a nod to the books. I'm not sure why the Tin Woodman had what appeared to be a furnace in his chest, but the film was pretty creative in its uses of the character's body. And apparently they can't have an Oz film without Winged Monkeys appearing in it, even though they were rather superfluous and there was no indication as to how the Jester got them to work for him.
I appreciated that the Queen of the Field-Mice put in an appearance, accompanied by a makeshift version of the Sawhorse. I entertained the notion that the bearded beavers who showed up in the same scene were Fairy Beavers, but that's probably too much of a stretch. I am interested in knowing whether anyone caught the names of the characters that the Jester had transformed into puppets. I think one of them was the Munchkin Mayor from the 1939 film, but I swear one of them was labeled as the Grand Bozzywoz of Samandra, a pretty obscure character from the books. If so, he didn't look much like his book counterpart, but I still give them credit for the reference.