My son actually picked up Holes first at the library. Since I was attempting to read in order, starting from the oldest, I hadn't gotten to it yet. But since he had it, I figured I'd read it. I'd previously seen the movie, and I must say that I much prefer reading and then watching a movie to the other way around. My sister ended up choosing this book for a Book Club she's with, and in comparing my feelings about the book in contrast with theirs, I could see how much of the anticipation and surprise of the twists I missed already knowing the outcome. That said, I appreciate how closely the movie parallels the book, because that is so rare in movie adaptations.
Holes has a surprising amount of depth (unintended pun, sorry) to the story. You don't expect that when you first pick it up. It seems like just another adventure story about an unfortunate boy sent to a work camp for a crime he didn't commit. But once well into the novel, you realize that there are deep themes of racism and interpersonal relationships expertly woven into the tale.
Previous posts have discussed how much subtle and overt racism earlier Newbery titles contain, as a reflection of their era. While these books can open a discussion about racism and its consequences, if such happens, it needs to be done in a deliberate manner. Holes on the other hand, vividly illustrates the ugliness of racism in a way that children can grasp without having to be led to the recognition. This might make Holes a good read before exposing your children to some of the earlier novels, so that your child can initiate a conversation about these themes making them more open to recognizing how behaviors and language in older books are not acceptable now, and were unjust then.