Oz is simultaneously a prequel, an independent story and a homage to the original Judy Garland Wizard of Oz film. Starting with the 'cardstock' titles, which I suspect are actually CGI, the movie tries to emulate the look and feel of the films of the 1930's. The homage aspect starts at the beginning where the Kansas scenes are filmed in black and white, as in the original. Oz is the traveling magician, with an assistant name 'Frank', in the 'Baum Brothers Circus'; a nice shout out to the author. And there is a brief scene where an old flame stops by to announce that 'John Gale' has asked her to marry him, nicely foreshadowing the heroine of it's predecessor. I'll also say that the city Oz as imagined in this film, seems to give a tip of the hat to Fritz Lang's Metropolis; which I believe carried over to the Disney castle in the credits.
I won't spoil it with too many details, the story revolves around this sideshow magician becoming the Wizard of Oz. The story itself may be new, I know that Baum wrote several books set in Oz, but haven't read them. The scenery resembles that of the original, but with all the powers of CGI behind it. The witch is wicked, the Munchkins are munchkiny and [spoiler] the flying monkeys are (mostly) baboons. They do a nice job of not letting the audience see the monsters the wicked witch has unleashed on the poor residents of Oz, which heightens the dramatic tension. There was one character development that I did not foresee, but which I heartily appreciated.
Now for the gaming aspect. After landing in the Oz, he has an encounter with 'river faeries'; these may help roll back the Tolkien interpretation of the fae as being wonderful enlightened beings. These are how the fae should be played, they have the sense of humor of an eight year old and they have teeth.
Baum's works are viewed (probably correctly) as geared towards juveniles, so they neglected as a source of inspiration in RPGs. This should be revisited by DMs, the flower orchestra is a masterful piece background that tells the characters "you're not in Kansas anymore". I suspect similar pieces exist in his works.