So clearly from the description you can tell this is a young adult novel and it's perfectly appropriate for young adult. Some YA novels (in my opinion) are kind of borderline with their appropriateness but this one is totally fine.
I got sucked into this book almost immediately because I really liked Poppy. The poor girl is essentially motherless, has a dad who tries but is pretty much at a loss, and feels set to the side by her step mom when her new sister comes along. I mean, that would be a lot for a teenager. And just when she feels the most on the outside, she gets essentially kidnapped by a Pixie and forced into a world she never knew existed. From there the story moves fast as she makes a friend after entering the Gloom and is on the search for her real mother so she can supposedly rid Winsome of the Gloom.
I love that it sucks you in, I love that you meet interesting characters along the way, and it's a fast read. I will say that so far, it really reminds me of Amanda Hockings Trylle Trilogy and that isn't such a bad thing. It does have significant differences but I was immediately reminded of that other trilogy. Which I haven't yet finished, so this should be interesting.