The job of all fantasy writers is to bring something new to the reader while also learning a bit from the history of the genre. Homer's epics are often cited as the two works that have defined Western fantasy even in modern books: the Iliad is the War, and the Odyssey is the Journey. While it's fun to stick to these concepts, the first thing I enjoyed about Beneath the Heavens was the fact that it doesn't focus at all on either of these. It's not even predominantly a murder mystery, although that factor is the main plot driver. No, what I took most out of this book was the relationship between the characters and their illnesses. Each one has a different case which brings out his or her inner qualities-good in some cases and bad in others-in powerful ways.
The fantasy world here is another enjoyable point. It's roughly analogous to the real world, with all the names spelled wrong, but done in a charming way. One thing that helps is the little amount of time spent dwelling on the functionality of the fantasy. Many modern authors butcher this aspect of fiction. When forced to justify fantasy against realism, it's easy to try too hard to make the fantasy seem realistic, when it's far more natural just to accept the fact that there's a dinosaur running next to your train, or that the term "miracle cure" isn't such an exaggeration.
I should point out that the writing style frequently didn't thrill me. Too often there are points of confusion between the semi-antique speech of the setting and the teenage slang of the main characters. Hardly anyone doesn't have an awkward-sounding line somewhere.
But to cap it off, the characters are great. Among my favorites are Karishma, an "Yndean" woman undergoing a complicated pregnancy; Tiernan, a teenager with severe schizophrenia; and especially Fritz, the socially-terrified engineer of the Miracle Line. The entire ensemble cast is great, once you can sort out who's who.
There you have it! I'd certainly recommend this book, especially to young writers who want to read a peer in action. For me, that's one of the best motivators there are.