There is nothing exactly new here, just par with the genre, but I quite liked it for being a lot less bloodthirsty than usual.
It was cute, and hopeful. There is much about life finding a way (the pea and the worm were beautiful, illustrative allegories), about greed, and how having and hoarding, and the pleasure of it harms, about the contrast between enjoying life and being serious about things, and how both are important, and how two people claiming each of these seemingly opposite characteristics can be true friends and team up successfully, about curiosity, and dreaming and trying to find new answers to old problems.
What I liked the most I think, was the positive influence of most adults present. Hell, even the antagonists give Lina a self-awareness eureka moment or two, but beyond that, most adults are caring, have good advice, are trying. It's very refreshing in a children book, where adults must be either absent, unfit or uncaring for the kids to have adventures.
I really liked it, will recommend it to mom's library's kids, and will try to get to the rest of the saga at some point.