Disclaimer I have seen the anime first (though only recently not when I was little) 

The beginning was VERY similar to the anime and I loved it! But towards the middle of the book there were so many differences that I got a little bit confused. 

The dog had a very different role and I missed the witch of the waste being old and frail because that was one of the most endearing aspects of the movie. Also she redeems herself in the end in studio ghibli‘s version. 

The scarecrow did have a much more complicated story in the book which I liked because it was more fleshed out. It‘s a lovely story and I like both versions though I do have to admit I like the anime a little bit more.