L Frank Baum wrote 14 Oz books, and I've read 6 of them.
The first one, despite all its shortcomings is by far the best.

I read them in the order they were written in. When I was on the second one, I suspected that the whole series was going to be a repetition of the original, and two chapters into the third one I was sure.
I'm ashamed to admit I carried on reading the rest because of my pig-headed author centricism.
These 6 are the only ones available as audio books from my libraries, so I'm joyously not reading the other 8. Oh frabjuous day, I said to myself when I was done with the last one.

In the preface to these sequels, the author attributes the story to his fans who "insisted" on more Oz stories. He also claims that he incorporated several of their ideas into these stories.
The Oz series is a perfect example of just why an author should not do that.
The first one was original, and that was the best thing about it. It had a number of inconsistencies however. Like the Tin Woodman who cries when a flower is plucked, but is happy to kill obviously more intelligent life forms like wolves and bees.
Everyone except Dorothy is already in possession of whatever it is they're seeking from the Wizard.
In my opinion, Dorothy was fully aware of this but kept this to herself and decided a bit of company would serve her well. Or they all knew, but wouldn't wish to admit it for fear others would challenge them on that point.
Tin doesn't rust. Iron does. Poppy flowers don't make people sleep.
However since the most general laws of physics have been violated in multiple ways during this, these are just petty and insignificant. (Here, general does not mean more or less true, it means absolutely true, in all generality)

Though I have only read 6 of 14 books, it is my theory that all books in this series can be condensed into the following:

quite against his/her intentions visits the land of being taken there by accompanied by . The protagonist wants to see so that they can . They take along who doesn't sleep and doesn't get tired or hungry.
They meet a mechanical man() who cannot sleep and who can't be hurt, cant get hungry or tired.

They are accompanied by a creature(lion/woggle bug/tiger/Jim/Button Bright/the Woozy and Bungle) who is dealing with a psychological problem -
They thwart
Only the protagonist gets what they were seeking.
The rest of them stay in Oz and they claim to be happy about it

Even some of the dialogue is repetitive :-(

This gets 2 stars only because of the first book, which was at least original

We get new characters and new parts of Oz in the first two but there's a lot of reused plots and the Patchwork Girl ends very abruptly with a quick fix that makes most of the story a pointless waste of time!

The Scarecrow of Oz is actually really good though.
I'm not sure why it's named after Scarecrow because he doesn't show up till halfway through!
It mainly follows Trot and Cap`n Bill who get sucked down a whirlpool and go on a journey with an Ork (weird, featherless, helicopter bird things). Hardly anyone tries to kill them and they help a princess and a gardeners boy to their happy ending.

Good female role models galore!

Love, Love, Love the OZ stories.

This has become required reading for my young niece, and any children in my future.

A wonderful classic for all ages. I enjoyed learning more about Oz and doing it for pleasure instead of class work. The Wizard of Oz is one of my favorite movies, so reading the whole story would be enjoyable. Fans of the movie adaptation should read this.