It's very much an allegory, and also very much a children's book. The morality is binary and explicit; the plot is straightforward (with more than a few too-convenient developments) and the characters incredibly simple. Lina is incredibly naive and reckless; Doon's main personality trait seems to thinking all the time. I couldn't relate to either of them, but I did manage some sympathy. That said, with so many more books to read I don't feel invested enough to finish the series, though I might at least consider it if my TBR wasn't so long.

Personally I thought the references to our world were a little too contrived - for example, the list of Mysterious Words From the Past - and the process of figuring "ancient" things out (

Spoiler

ie, candles, matches, boats

) was either too drawn out or so abrupt as to stretch disbelief.