My thoughts on just reading the book will be characteristically scattered.
First up: what a death toll!
Spoiler
There were some noticable themes running through Reaper's Gale, though I can't quite pull them together into a coherent whole, I have my ideas--sex, power, friendship, and love were prominent, leading me to think that the key thing in this book is relationships. Relationships of all kinds, in all forms: Rhulad and Nisall, Rhulad and his advisors. Atri-Preda Bivatt, Bohl Handar, Letur Anict, and Orbyn Truthfinder. Karos Invictad and Tanal Yathvanar, Tanal Yathvanar and Janath Anar, Janath Anar and Tehol Beddict, Tehol Beddict and Bugg, (Tehol Beddict and Karos Invictad,) Bugg and the Errant, the Errant and Feather Witch, Feather Witch and everyone who uses her without her even realising it.
Relationships of love, lust, power, and friendship.
Certainly a very fitting continuation of the series--personally, I'd say it most resembles Memories of Ice in content, though it steps things up a notch. And being a direct sequel to both Midnight Tides and The Bonehunters--with various connections also to Memories of Ice--it ties things together very nicely.