I picked up The Book of Three on the suggestion of my husband, who had enjoyed the Chronicles of Prydain series as a kid. In a Welsh-inspired land, an Assistant Pig-Keeper longs for adventure and the chance to be a hero. When he loses his pig (who happens to be an oracle), he gets even more adventure than he bargained for. As he tries to find his oracular pig before the pig falls into the hands of an evil king who threatens Prydain, he meets a strange and loyal creature, a king-turned bard, a real-life hero, an evil sorceress, and a sassy princess. He faces fears, makes friends, and learns that heroism isn't exactly what he thought it was.
I liked The Book of Three, and am currently enjoying the rest of the Chronicles of Prydain. It's classic quest fantasy, and although there are no real surprises or twists, it's classic done well. I appreciate that the characters grow throughout the story and series as a whole, although a few of the "lessons" that Taran learns are a bit "lessony." There's a whimsy to the books that I enjoyed as well, and I think they'd be great books for a family to read aloud together. They are definitely books I'd hand off to kids looking for fantasy, and as an adult it's an easy, comfort-food kind of experience.
Bottom line: a solid, Welsh-flavored, children's fantasy story.