The sheer span and scope is mind-boggling - in a good way. In a GREAT way, in fact.
I still can't get my head wrapped around how Ryan was able to put together such an expansive story with so many characters and information and keep it fascinating page after page. To me it's like part military history text of World War II (and I love that stuff), part steampunk novel, and part grand epic fantasy, all made to work in a way I would have previously thought impossible. This series, and particularly The Empire of Ashes, carries us through breathtaking campaigns all over the world, by land, sea, and air, while also describing the fascinating political, economic and technological military industrial developments akin to both that WWI and WWII - but add to that dragons, sea monsters, magic, and armies of the undead. I'm simply amazed. More so because the characters never get lost. They're front and center all the way through.
Speaking of the characters, I can't remember a book where they were more complex yet interesting. Ryan's ability to craft them and bring them to life is masterful - particularly in that we see our hero's sometimes do terrible things, and the most despicable characters at times do the most wonderful things - and most times when we least expect it. Friends can become our worst enemies, and enemies can become the most stalwart allies. It just feels real, but still with that sense of fantastical wonder we all crave.
As a final note: Without giving anything away, hats off and a deep bow with an ear-to-ear grin for the name given to one of the aerostats (from one of my favorite television shows of all time). Hint hint, nudge nudge, say no more...