My only prior experience with Lloyd Alexander is the rather terrifying 1985 Disney film The Black Cauldron. I've watched it multiple times and still don't really like it. I was hoping that I might feel different about the book series, The House of Prydain, that the movie was based on.
Taran is an assistant pig-keeper for a pig named Hen Wen who can somehow tell the future, so she's called an oracular pig. Long story short, the Horned King is a terrifying enemy and a servant of Arawn, Death-Lord of Annuvin. When The Horned King comes close to Taran's home, all the animals make a run for it, including Hen Wen, and Taran, loyal boy that he is, chases her. He has one adventure after another, bumping into the cornw prince of Prydain named Gwydion. They travel together for a while, still searching for Hen Wen, but also now needing to reach Caer Dathyl, a home castle base as it were, of the Horned King's movements. Enter Gurgi, a bizarre, half-human and half-animal creature who is surprisingly loyal to Taran and Taran's develops a fondness for him, especially when Taran provides him with his "munchings and crunchings" as a reward for his help. There's a capture that happens, Taran's locked up, he meets a girl named Eilonwy who is by far one of the most annoying female characters I've ever encountered, but she manages to free him. It really just goes on and on, so for such a short book, it crams a lot into it.
I really wish I could say that I liked it, but all the way through I couldn't stop thinking that it was a poor substitute for Tolkien's The Lord of the Rings. I mean, it really is a bit of a knock-off. Maybe that wasn't Alexander's intent, but that's what happened, even down to these flying creatures who serve the Death Lord and Gurgi, who's a slightly tamer version of Gollum. It's interesting, but as a child if I'd read it, I wouldn't have liked it much. I don't like the idea of oracular pigs and word sticks being used to tell the future, especially not in children's fiction. And I genuinely disliked Eilonwy, the lone "good" female character. That girl prattles and rattles and believes she knows best and holds grudges, and is just downright obnoxious. She's arrogant and insufferable and one of the reasons I dislike her is because some of her traits are some of the ones I don't like about myself, so yeah, they always say the characters we dislike the most are the ones we resemble (even if it's just slightly), so there you go.