ISTG, I'd read the phone book if Ursula wrote it.
I've mentioned this before, but some writers seem to have a direct line to my heart and they can just reach in and grab my heartstrings and yoink!
Ursula is one of them. Everyone else has already said the good stuff about how she wrote a middle grade portal fantasy for adults that takes the best of both genres and combines them. More than that, I find Ursula has a gift for stepping back from both the glorious emotional triumphs that authors like CS Lewis use and equally devastating emotional tragedies that often drive more adult materials. Instead, she finds meaning in the small things and takes the middle road and the ordinary and celebrates it into its own kind of extraordinary. And I love her for it.

The reason this book works, and it does, is that the author has a VERY good sense of what to take seriously and what should be handled with great silliness.
The premise is silly and Flynn clearly knows that. But the details of the early 19th century are elements that Flynn takes very seriously - time travel can be wibbly wobbly, but we need verisimilitude in our inns!
That's the thing - the balance is good. And Flynn conveniently writes from the viewpoint of a modern character, so all the first person reflections can use a contemporary voice and not fall into the trap of trying to be Jane Austen. Flynn only needs to get Austen's dialogue right, she doesn't need to get Austen's free indirect discourse. The latter is...really really hard, let's say.

Also, the main character is Jewish. For no reason other than that Jews exist and do things in the world so why shouldn't the main character be Jewish? And I appreciated that.

I don't remember who coined the term cozy space opera (I think it was one of the galactic suburbanites) to discuss Chambers' work, but it absolutely qualifies.
I almost wish I had read this before the Hugo noms came out and I wasn't reading it to evaluate it (or reading it over that ridiculous watermark: My research kinda suggests that interfering with the novel reading process leads to a less enjoyable text...I wonder if publishers realize that the logical conclusion is that watermarking books hamstrings their ability to win). Chambers is still a delightful read and though the book itself was somewhat awkward with pacing, the meat of the characters and grappling with sentience more than made up for it.

Hmm, either sf is less dated by decade than fantasy or I'm not familiar enough with the genre to pinpoint the fashion the way that I can for, say, 80s sword and sorcery.
There is something timeless about this story; it touches on so many elements that preoccupy the SF world at the moment, albeit without the contemporary need for subversion. It works in this story, perhaps because it is also a retelling of a fairy tale, and thank you to Tor's space opera month list for suggesting it.

I liked this book very much, but I also wanted to love this book and I didn't and that was frustrating. I love 19th century speculative fiction, I teach Frankenstein often to my undergrads (and the Frankenstein bits were possibly my favorites), and I completely appreciate what Goss is doing here. Her premise is glorious. Her execution falters slightly. Partially, that's because I found the narrative choice to have the characters interject their comments into the manuscript annoying. I get what Goss was going for and I appreciate it as a kind of meta-comment about narrative and truth telling, but it interrupted the narrative's capacity to enchant me and I felt distant from it. It also hit the uncanny valley of 19th century style for me: close enough that it sometimes felt right, but then someone would say something that felt off and suddenly everything looked wrong. Is there an uncanny valley for language even?
I'm hoping the second book is slightly different and Goss, moving on from her debut novel, has a slightly surer voice and pacing to the narrative.

(My first review got eaten by my wifi and now I'm sad.)
This series. In some ways, this review is for the entire thing and for Newman totally sticking the landing and successfully pulling everything together. I was about 1/5 of the way through and watching her unravel ends that had already seemed tidied up and wondering how she was going to finish it all in one book, but she did it, weaving everything in and getting it off the needles before it grew too big. (Here endeth the knitting analogy.) I really enjoyed it; it's exactly the sort of urban fantasy I like reading: clever, British, and feminist.

But I have to talk about Will. Because he really is the hardest character to get right and Newman just does it effortlessly. The question is not whether he is the villain of the story (or at least a villain. Everyone's the villain at some point) but whether he can successfully sell us as readers on his vision of reality. Being inside his head is disorienting because Newman shows us how his justifications work and his remorse and all the good things he does. She shows us how evil happens at the hands of those who don't see themselves as evil and who deeply regret it. It's up to us--and to Cathy, who has been Will's victim one too many times--to see through him and to recognize how well meaning people who would never see themselves as evil still do horrible things. The book asks us to think about how we deal with people who mean well and do ill, who lack evil intentions, but create evil consequences. And it answers, rather brilliantly, destroy the power structures that let them perpetuate their evil. It's not about punishing Will; it's about making sure no one will ever be in his position again.

There's a reason that I consider The Split Worlds to be paradigmatic of a story trend I've seen recently. I've been watching the growth of what I think of as Social Justice Speculative Fiction - that is SF where the concerns of the plot are deeply imbricated in issues of social justice. (I cannot believe I have to add this disclaimer, but) This is not derogatory; on the contrary, it's an example of SF doing what it does best, speculating. As speculative fiction, it either predicts or mythologizes elements of the world we inhabit in order to better understand the way that the world works. Fantasy, in particular, is no longer merely the genre of the mythic past that idealizes The Return of the King, but equally the genre of the mythic present via defamiliarization, holding the fun house mirror up to life to reexamine what we thought we knew about war and colonization and feminism and queer representation. It's a brilliant achievement and (speaking of disclaimers I shouldn't need) makes for better crafted narratives with more polished prose than the tired rehash of the Hero's Journey. Newman's work fits into this form neatly and for that I love it. But Newman's social justice fantasy is also fundamentally the fantasy that magic can be a force for social justice. Spoilers for both Split Worlds and Wonder Woman ahead.

Newman links the splitting of her worlds with climate change, much like Wonder Woman links humankind's propensity to war with the God Ares. And Diana's confrontation with Remus Lupin Ares serves partly to give her an enemy in her weight class and partly to undermine the idea that magical force fighting for the side of good is enough to fix things. Not entirely; Diana is still a SJW of the highest order and the movie is still something of a fantasy about having the magical power to fix things, but it does complicate that vision significantly. Newman mostly plays it straight: in order to fix climate change, you need to bring back the Fae and they will balance the elemental court. Not perfectly, but they make it possible. And it works in the story, but it does leave me wishing to set Lord Poppy on everyone in power not currently working to fix things...

Welp, that's a first. I have never had something jump my Hugo rankings from last-thing-read to #1 before.
LaValle has an exquisite sense of pacing and, while I would describe the writing as good without being showy for the first third, the story and style suddenly explode and you get the sheer genius of the earlier understatement. LaValle's writing is sometimes gut-wrenching in the way that makes you both afraid to keep reading and equally terrified to stop.
I hope this wins.

So once I got the first book in last year's Hugo packet--and read it--I couldn't NOT finish the series. Naam's approach to the technothriller remains compelling. I really like the nuance he brings to conversations about the post-human, uploading brains, and the way that control functions. He clearly has a specific ideology and occasionally slips into the trap of making the good guys a bit too good in that you don't quite see the ramifications of their choices. His bad guys doing what they think is right, however, are perfectly chilling. It's tough - I want an uplifting resolution in the third book that doesn't sacrifice the complexity of the questions in the narrative. No pressure, then.

I wanted this book to be better than it was, which is weird, because I also have no idea what was wrong with this book. I can't point to anything--it's a history with few villains and little conflict, but I liked that about the book--and I found the topic compelling, but it didn't grab me. There was no momentum to the overall narrative even as the stories themselves were impressive achievements. Linked short stories might have worked better.

Is "dammit, Seanan!" a complete review?
This is one of the few prequels that you have to read after the original because the ways in which it is heartbreaking depends on Every Heart a Doorway and the ways/places of being established in that book. But it's shiningly brutal in its own right and I love Seanan when she's writing in fairy tale mode. I may need to go back and reread "How the Maine Coone" now to make myself feel better.