The world Beagle creates is in an in-between state, one where legends and magic are fading and the world is becoming the mundane one we know. Unicorns themselves are timeless, preserving a bit of that magic and fairy-tale reality wherever they live, or wherever they go...but with them almost gone, and the last traveling on her quest, we see the world shifting between one in which butterflies sing everything from Shakespeare to advertising jingles to a more ordinary one and back again. And then there are a few characters who understand the structure of stories, and what it means for the spells, prophecies, and other challenges they encounter.
The characters are well-drawn, too. The unicorn herself has such a different perspective on life and time, and it's hard to fault her trustingness (it isn't quite naivete) during the early part of the journey. The incompetent magician Schmendrick manages to shift by turns between pitiful and insufferable. Molly Grue, a character I don't remember at all, is in some ways the most relatable: She's an ordinary human, no magic, no expectations on her, but she sees things as they are, sees what needs to be done, and does it. And after the unicorn is transformed into a human woman, and they find themselves in King Haggard's castle, it's heartbreaking to watch Amalthea lose her true self bit by bit. Haggard himself is an odd villain, one whose success has broken him, causing him to sink into despair long before his castle will sink into the sea.
But in a sense neither Haggard nor the Bull is the real villain: it's despair itself, and the desire to capture and hoard wonder. Because holding wonder captive destroys it.
Cross-posted from my website, where I also add some background on how I ended up finally reading the book.