I was taken to The Wizard of Oz when I was 6 or so (in one of the big old theaters in the Chicago Loop, early 1950s) for what must have been its last theatrical reissue before it became an annual staple on TV. I had already read the book, precocious brat that I was, and like any kid that age had very decided expectations about how the book should be filmed. I kind of knew that they couldn't include everything, so I adjusted to the streamlining of the story, didn't mind the songs too much, thought the move from B&W to color was a thrilling idea, and positively enjoyed the performances -- especially Garland as Dorothy, Ray Bolger as scarecrow, Bert Lahr as the lion (though I was too young to understand the vaudevillian aspects), and Margaret Hamilton's witch. Even now, with my adult eyes, I can't see much wrong with any of the performances. I mean, Billie Burke is in no way my idea of Glinda, but I can't blame her, as that was her invariable screen persona; so those in charge must have wanted exactly that.
No, the things that bugged my 6-year-old self were the alterations from the book for which I could see no point: the endless initial sequence in Kansas (Baum has the house in the air by the second page, and the gimmick that all those actors would later reappear in Oz was lost on me), the changing of the silver shoes into ruby slippers, the conflation of the Good Witch of the North (who greets Dorothy initially) with Glinda, and most unforgivably (even now) the idea that the visit to Oz was all a dream. No. It was real. (And in a later book Dorothy, Em, Henry, and Toto go there to live permanently.)
Despite those objections, I still love the movie.