It's kind of a neat idea: a prequel to The Wizard of Oz, showing how the Wizard made his way to the enchanted land. (A remake of the original would be kind of sacreligious, I guess. Millions of Judy Garland fans would bitch and moan about whoever played Dorothy, for one thing.)
James Franco plays the future Wizard. His humble beginnings are as a Kansan carnival magician/con artist, and his highest ambitions are to make some semi-dishonest cash and have his (PG-rated) way with a lot of women. (As in the original, these real-world scenes are monochrome; they're also in 4:3 aspect ratio.)
An outraged husband causes Oz to (literally) take flight in a handy circus balloon: a good plan until he runs into the inevitable Kansas tornado, which whisks him to Oz, where things are colorful and widescreen. There he meets the good and evil witches (Mila Kunis, Rachel Weisz, Michelle Williams); he has a hard time telling which are which, though. He also picks up a couple of travelling companions: China Girl (a talking doll) and Finley (a flying monkey, but a nice one). An epic struggle develops between the forces of good and evil over control of the Emerald City.
The movie is directed by the great and powerful Sam Raimi, so it's not bad. It was a 3-D production in the theatres, and there are a lot of visual gags that came off flat (heh) on my exceedingly normal home TV. There are a number of clever homages to the original movie, but intellectual property rights apparently limited the links that could have been made. (No Scarecrow, Tin Man, or Cowardly Lion backstories, sorry.)