One of those fantasy classics which I had never actually read, though of course I've seen the 1939 film numerous times. Naturally the first thing that strikes me is the number of differences between the two:
Dorothy is much younger in the book - the original Denslow illustrations show her as a very little girl, Alice-size or smaller.
She is also more passive than in the film (which gives the scarecrow, lion and woodman a bit more character development).
Oz is a distant part of our world, not a dream (so Uncle Henry and Auntie Em have to rebuild their house after the cyclone removes it).
The Kansas section at the start of the book is very short, and the section at the end even shorter (half a page).
The Wizard interviews the four travellers separately, when they arrive in the Emerald City, and appears different to each of them.
The Emerald City isn't all that green - residents and visitors are forced to wear green-tinted spectacles.
The magic shoes are silver rather than red.
Dorothy and friends encounter a country populated by living china figurines and another populated by sinister "Hammerheads".
There are no songs.
It is generally pleasantly and confidently well-written, and I'll pass it on to nine-year-old F with a strong recommendation; I think he will enjoy it, and I can see why it is a classic.