Some Bits and Pieces about the Book
The series focuses on Elphaba, the woman who becomes the Wicked Witch of the West. Instead of her being purely evil, Elphaba is a complex, misunderstood, and morally conflicted characters. The tone is dark, mature and political. Some major themes in the book are good vs. evil, prejudice and discrimination, power and political corruption, and identity/self-acceptance.
If you are a fan of the musical or movie, the book might be worth reading, but you should go in with the expectation of a darker tone to the story. I'd recommend the book to someone that likes morally gray characters, enjoys dark and mature fantasy, and have an appreciation for social commentary.
The Play and Movie
These adaptations of the book are lighter in tone and more family-friendly. They focus more on the themes of friendship, love, and humor, but still touch on the serious themes in the book in a digestible way. These adaptations also simply the story to focus more on Glinda's and Elphaba's friendship.
These adaptations have omitted, changed, and condensed events in the book for mass-audience appeal and pacing of the story. They basically focus more on fun and humor.
Wicked Movie
Wicked Play