The way L. Frank Baum and W.W. Denslow designed the book was rather elaborate. Since the book was a novel and not a picture book like Father Goose: His Book, they found a new way to mix the text, illustrations and color.
The design involved multiple colored inks as well as black, not to mention twenty four color plates. There would be sections of the illustration printed in black and sections printed in color ink that would appear under the text. Furthermore, the color of the ink would change with each location of the story. A dull brown for Kansas:
Denslow's illustrations are also to thank. Although his Dorothy doesn't look quite so girlish, she is not ugly and the rest of the characters are very charming. Denslow also doesn't draw the giant spider or the Wizard's form as a monstrous beast, and the Wicked Witch of the West has been given some comical details to soften her character. (The umbrella, eyepatch and pickaninny pigtails.)
No child would have nightmares from Oz. No chapter ends with a cruel beast or witch coming after Dorothy, and if there is bloodshed, it is not dwelled on. Denslow's pictures only help accentuate Baum's storytelling.
The Hill Company was once again hesitant to publish Oz, but Baum and Denslow decided to put their royalties from Father Goose: His Book into helping defray production costs, a gamble that paid off very well. The Wonderful Wizard of Oz remained in print until the Hill Company closed.
The plates and rights for Baum's books were bought up by the Bobbs-Merrill Company who issued a number of Baum's later books until Reilly & Britton came onto the scene. Following the success of The Wizard of Oz stage extravaganza, Bobbs-Merrill redesigned the book. It still used interior color and Denslow created some new artwork for it, including a new title page and endapers, but it was not quite as lavish as the original edition.
Perhaps the difference in design was why the original Bobbs-Merrill edition was called The New Wizard of Oz. Shortly after, Bobbs-Merrill changed the title to simply The Wizard of Oz, a name the book was published under for a very long time. In fact, it does not appear that the word Wonderful was added back to the title until after the book went into public domain.
Later editions of the Bobbs-Merrill Wizard of Oz became even simpler, interior color quickly being dropped to keep the cost of reprinting it low. Eventually, this led to the first re-illustrating by Evelyn Copelman, which opened the door to other artists creating new illustrations. While many fine artists have put their talents to Oz, none have matched the same charm Denslow produced when he and L. Frank Baum designed a novel for children that would never give them nightmares. Although John R. Neill would later succeed Denslow as illustrator for Oz and created amazing artwork, the fact remains that he never had the same relationship with Baum as Denslow did. While many have wished that Neill had re-illustrated Wizard, sometimes, I feel it is best that he left the book alone.
The original edition of The Wonderful Wizard of Oz is indeed the most lavish the book had ever looked, and it is rather easy to contest that this is how author and illustrator wanted the book to look. The beautiful volume delighted many eyes in 1900 with the colorful pictures and a wonderful story. It was Denslow's success just as much as Baum's for creating such a great book.