I'm just gonna say it now: this book didn't really work for me. Sorry about that. There is a ton of action and interesting worldbuilding, and if you can get pulled into the story, I think it could be a lot of fun.
Oddly enough, I suspect that the core of my discontent can be traced to the omniscient third-person narration. With these types of books, I think I've really come to prefer first-person narration. For one thing, first-person narration adds an additional layer of unreliability between the reader and the world, and this insulation can be leveraged whenever the reader and the narrator disagree. If Harry Dresden tells me a character is all-round awesome and I disagree, I just roll my eyes and chalk it up to Dresden's unreliability, as I only believe him a tenth of the time anyway. When Butcher describes Grimm as all-round awesome, then I've been put at odds with the author and I end up feeling exasperated and increasingly put upon because seriously, apart from anything else, why would you give your character that surname? The same is true for what I might term Butcher's narrative tics. Granted, it drives me somewhat nuts when Dresden overuses "arched an eyebrow" and "shambled" and all the rest, and I long ago decided that there's a potential drinking game there, as long as no-one minded the alcohol poisoning. But it's a whole other level of irritation when the eyebrow-arching is third person because there's no buffer between me and the author.
So much of Butcher's trademark writing works better in first person. For example, he tends to pause before the characters take action to fully describe the alternatives and the risks, and I think that works quite well when it's the character panicking about their possible choices. But in third person, I found it a bit tedious. Don't get me wrong; I loved Codex Alera, partly because it felt so lighthearted compared to most of the epic fantasy out there, and partly because it took so much joy in utilizing and subverting various tropes, and it's third person. But possibly because I don't even read enough steampunk to be weary with it,The Aeronaut's Windlass just didn't hit me the same way.
I really wish I had warmed to one--any--of the characters, but I just couldn't manage it. Grimm is too much of a one-dimensional Wronged Hero, complete with tragic past and noble intentions. Benedict is Misunderstood Hero Number Two,Special Inhuman Powers included absolutely free of charge. Bridget really needs to stop dithering. Gwen might have been fun if she was first person--I kind of love imperious female characters; please don't consider that too deeply--but she combined her haughty manner with such an impressive level of myopia and coldness that I just couldn't feel much for her. Worst of all, I should have adored the talking cats, but I just didn't. To me, it felt like Butcher didn't capture enough catty quirks and body language, but maybe that's just because I'm primarily a dog person. I quite enjoyed the etherics, however. Their impressive level of amusing oddity added a great deal of color to the story.
So what is there to love? Well, I thought the worldbuilding showed a lot of promise. People living far above the apparently postapocalyptic earth? Yes, please. And no matter how much others might sneer, I have no personal beef with either airships or trenchcoats. Taking a tired trope and making it new can be a lot of fun, and even though I can't visualize them at all, I thought Butcher's airships seemed fresh, partly because I don't think they share a lot with a traditional ship in the first place. I'd love to know precisely what sent civilization into the clouds and mutated the world underneath, but sadly, I'm not sure I'm willing to push through another book to find out.