Oz The Great and Powerful

I'm not a fan of unnecessary sequels, so imagine how I feel about unnecessary prequels! Well, Oz The Great and Powerful is definitely an unnecessary predecessor to a timeless classic, The Wizard Of Oz.
Before I discuss the film, it's worth thinking about the merits of it first.
Consider this, Oz and all its characters exist only in the imagination of Dorothy Gale thanks to being knocked out during a tornado. Only then was she transported to this wonderful, colourful land.
So then, how can we have a prequel to a dream when Oz is only a figment of Dorothy's imagination. What they are asking you to do is buy that the Wizard was transported to Oz well before Dorothy was born by a similar tornado journey. Please.
That aside, we have Oscar Diggs (James Franco) who is a small time Kansas magician and con man. He's sent to Oz in a balloon trying to escape from carnival people who have caught up on his dallying with women.
When he arrives he is met by Theodora (Mila Kunis), a witch whose motives are unclear but who falls for the man she proclaims the wizard who was prophesied to arrive and save Oz.
Along the way to the Emerald City, Oz comes across Finley (Zach Braff) a monkey (who looks a lot more like the winged monkeys in the Wiazard of Oz than the actual bad monkeys in this one) who pledges himself to a life of servitude for being saved.
On arrival at the city we meet Evanora (Rachel Weisz), Theodora's sister, who quickly shows her evil side in sending Oz to kill the 'wicked witch' after promising all the riches of Oz to him when he takes the throne as Wizard.
This wicked witch is Glinda (Michelle Williams) who we all know to be the good witch of the north.
Anyway, there's also a china doll character that comes along for the ride in one of a few tie ins between Kansas and Oz similar to what you see in the original.
The first thing you notice about Oz is that its been given an overdose of CGI. It just looks far too over the top. Also, we don't see any ruby slippers (apparently due to a copyright issue) that the wicked witch of the east possess.
There's pretty much just one song and Oz cuts the munchkins off half way through, the makers obviously weren't looking for a musical, and as much as I like him James Franco might have been miscast.
The witches are excellent, Finley is great comic relief at times but overall it has all the hallmarks of an unnecessary prequel, particularly since it is not allowed to be linked to the original.
Probably because The Wizard Of Oz is such a great film it's hard to get into this overproduced, overly long and virtually soulless movie. Ironically, it's saved by the witches and that's largely why I went 6 out of 10.
Maybe they should have done a movie version of Wicked instead, I didn't need to know how an imaginary wizard, who couldn't have been in Oz in a world without Dorothy, made it to an imaginary land.
But maybe I overthought it...