Unintentional Period Piece: Norton Juster noted that, in the 21st century, tollbooths have fallen into disuse and aren't so common as they were in the time his novel was written.
Values Resonance: In the "appreciation by Maurice Sendak" that accompanies the Yearling edition of the book, Sendak notes how the monsters and obstacles in the book are "prophetic and scarily pertinent" to modern living and how Juster's "allegorical monsters have become all too real".
Before he properly drives through, Milo spends a couple of minutes just screwing around with the tollbooth, watching how his live-action and cartoon selves interact with it for no other reason than to show off the special effects.
Chroma the Great conducts the sunset and Milo plays music in his stead, which causes the sky to become chaotic. Even though the colors are messed up, Milo, Tock, and the Humbug simply drive off. The only thing to come out of it is that it hints of the necessity of Rhyme and Reason to fix the instability brought on the indirect influence of the Demons.
Tear Jerker: Tock's Heroic Sacrifice against the combined Demon of Ignorance, with Milo not even allowed to properly mourn his potential death in order to rescue the Princesses. Especially, so as Tock was his first friend in the world and helped him out of his bored way of life.
The initial intro song of Milo, which details how uninterested Milo is concerning life in general, having a mellow and melancholy tone.
Milo having to leave the world of the Tollbooth with a greater appreciation for knowledge as the Tollbooth goes to another child's home so they can have their own journey. While he did save that world, the inability to see his friends again is very saddening.
Visual Effects of Awesome: Chuck Jones of Looney Tunes fame, brings the world of the Phantom Tollbooth to life with his usual elegant yet comedic designs, but also experiments with a variety of styles for the various characters to create designs for characters that drastically differ from his usual expertise, ranging from the heavily scratchy designs for the Demons of Ignorance, the marker look of the Awful Dyne, and the liquidy Lethargians.
The background images are also intricate and beautiful to look at, combining elements of alphabets, numbers, etc.
