This is my favorite children's book. There are so many things about it to adore I don't know where to start, so I'll go with what I've learned over the years as a result of this book.
Dick Gackenbach was a genius. His approach to low-color art and design is lush and textural. His understanding of the page space and the depth of the field his characters live in is as good as Sendak's, but his approach to storytelling is arguably better. His accessible but beautiful characters are alive, but clearly simplified illustrations at the same time. Economy of line, clear contrast, and spot colors to draw you through the world. Modernist design of the Eames caliber condensed down into something for everyone.
Harry projects amazing values and solid judgement and bravery in a way I aspired to as a kid, and as an adult. He knows the dangers, but finds the right tool for the job and sets to solving the problem. He stands by his family and cares for is mother above himself. Harry feels deep compassion for the Whatsit and sends him on his way with a solid lead on a new house to live in, right next door.
You really understand Harry's perspective on the world in this book. You feel like a kid yourself, it's nostalgic and primal at once.
This is a book held in very high regard in my house. I wish there was a way to thank Mr. Gackenbach directly, but this will have to do. Thank you, Dick, you made a big difference for me.