Wow. That is all I can think just having read the book. Its based on Edgar Allan Poe's novella The Masque of the Red Death, which I read before this book knowing that that was what it was based on. I didn't really think that there was much substance in Poe's version, though it has given me a good idea of what may happen in the sequel, Dance of the Red Death.
At first I found it difficult to determine what time period the novel was set in, eventually I decided on early 19th century because of the mentions of steam carriages replacing the horse drawn type when all the horses died, the lack of any technology, mentions of how modest fashion was adapted to show as much skin as possible, and the mention of being chaperone-less (and being young and female). Despite it seemingly being set at least 100 years ago, the novel doesn't feel out of date in the slightest (though having been released last year it would have struggled to!)
EDIT: the goodreads entry for Masque of the Red Death, informs me that it is set in 1870
The dystopia itself was interesting, as with Poe's original version it is set off by a plague that causes people to weep blood and pus, add to this Prince Prospero and his wish to control everything and everyone and there is a powerful dystopia on all fronts.
The characters had the right amount of depth, Araby really felt real, and her emotions went through a real range of emotions, from grief at the death of her twin (happened pre-novel), her confusion over the opposite sex (not just specific people but in general), her fear of dying, her wish for 'oblivion', it all adds to her. Similarly I enjoyed how April developed throughout, and when she 'changed' personality (albeit only slightly) it didn't feel like it was just a plot point, it seemed natural.
Another notable part of the characterisations was how believable the desires to overthrow Prospero were for both Elliott and Rev. Malcontent, it doesn't just feel like rebelling for rebelling's sake.
The only bad thing about this book is that the sequel isn't available til June! Well and the fact that I can't seem to find a copy of the ebook novella Glitter & Doom to read!