Short version, i liked it, but it is _very_ different from all the other Vorkosigan novels.
Slight spoilers as to the nature of the book. Explicit spoilers about the history/back stories of character relationships. (Er... not THAT kind of explicit!) And also blatant spoilers for events in earlier books, duh.
First, some minor issues.
So at the start i was kind of bothered by Jole's relationship with Aral, not because of the same-sex aspect but because it seemed like it just came out of nowhere. However after the first chapter or two i searched around on the internet a bit and found this tumblr post: http://dsudis.tumblr.com/post/115697353364/i-was-right-ask-me-how
After reading that i was pretty content with the relationship status as described in the book.
Some people are apparently up in arms about the way their relationship started, declaring that Aral cheated on Cordelia with Jole while she was off planet.
I don't have the text handy but i definitely had the impression that Cordelia and Aral had talked about his feelings for men before and Cordelia has been encouraging him to do something about it, egging him on about whoever his latest fancy was in fact, including Jole. As such it seemed like at the very least he already had implied permission to hook up with someone else, possibly even explicit permission. (I've been in poly relationships in the past myself where that was certainly the case, so perhaps that informs my perspective.) It does seem like that part was glossed over pretty vaguely in the text and it might have saved some trouble if Bujold had dropped in another sentence or two making that clear.
But now for the elephant in the room. ("Money, power, sex... and elephants." But i digress.)
From the beginning of the series (Shards of Honor) the Vorkosigan books have been about interplanetary intrigue, adventure, romance, and general (but very excellent) commentary on the human condition. The romance aspects _mostly_ took a back seat during Miles' career as a mercenary/ImpSec agent, but came back with a vengeance (and a warm welcome!) in Komarr and later books.
Gentleman Jole and the Red Queen has the romance and human condition aspects.
For at least the first half of the book i kept thinking "ah, is this the hook that will kick off the intrigue part of the plot?" But it never did. A lot of the "hooks" got resolutions at the end, but very mundane ones. Is it an oxymoron to say that one of them was resolved by a deus ex machina that was obviously telegraphed? I guess that makes it more of a (non-military) The Cavalry?
Instead it's all about the relationship between Jole and Cordelia. (Is it a spoiler that they have a relationship? It's implied in the bloody title, so i don't think so.)
It's also worth pointing out that, although the book certainly isn't devoid of humor, there's nothing like the dinner party from "A Civil Campaign" in it.
I think sithjawa stated it best on twitter, "It's a very placid book. To me it reads like the end of Return of the King. An epilogue or victory lap."
But it's also worth specifying that it's more like the _movie_ end of Return of the King. In the book version they had to deal with the Scouring of the Shire. In the grand scope of the series the Scouring was a pretty minor event (one might almost call it a footnote, hah) but it was still a challenge the Hobbits had to face and overcome.
Jole's only challenges in the book are midlife crisis style "challenges". And Cordelia's "challenges" just aren't. One of them was so minor that it literally went away because she ignored it.
In "Shards of Honor" and "Barrayar" Cordeilia was a well developed protagonist. She had strengths and faults and challenges to overcome. When the books switch over to Miles as a protagonist she became a parent figure. She was a wise and caring mother who always had a good answer for anything and was always right about everything. Which was okay for someone who was now a secondary character, especially one often being viewed through the lens of her affectionate (if also sometimes exasperated) son. In effect she acted as a foil for both Miles and Barrayar whenever they were screwing something up or making it more complicated than they needed to. Which was just fine for the role she was playing.
So now she's the protagonist again, but she's still practically perfect in every way and she doesn't have any _serious_ challenges to face.
Someone pointed out something that Bujold has said in the past:
"I have a catchphrase to describe my plot-generation technique — 'What's the worst possible thing I can do to these people?'"
And that clearly just wasn't part of the process for this book.
I forget at exactly what point i started hearing that Bujold was emotionally done with the Vorkosiverse but kept being pressured to write more, but it was certainly several books back. Given the evidence it seems most likely this state of affairs arose sometime after "A Civil Campaign".
So to me it feels like that more and more as time has gone on Bujold has still been succumbing to publisher pressure, but using the opportunity to get closure with the Vorkosiverse rather than writing "normal" books of the original style. A book about Miles' life post-marriage, a book that is practically a meditation on the nature of death and loss that (predictably) ended with Aral's death, a book that went out of its way to avoid dealing with the emotional fallout of Aral's death and instead provides closure to Ivan's life as a footloose and fancy free single guy, and finally a book that gets back to the repercussions of Aral's death and moves Cordelia on to the next stage of her life.
It's notable that (arguably) each of those books has had less action and intrigue than the one before it. I'm guessing that's not what the publisher wants, but i suspect their ability to strong arm her into more Vorkosigan books is getting weaker over time. And since i haven't said it already, i think this is probably my least favorite of all the Vorkosigan books so far, though a reread _might_ change that. However "least good of all Vorkosigan books" is... praising with faint damn?
And in an aside, it's also been claimed that Bujold's publisher was not happy with the homosexual themes of "Ethan of Athos" and didn't want any more books like that. If true that might provide some explanation for why the Aral's relationship with Jole has barely even been alluded to before now, and why she's only explicitly brought it to light when A: it's being discussed posthumously, and B: she practically has her publisher over a barrel.
In any case, if Bujold wants to write more Vorkosigan books in this style i'll certainly read them, but i won't be looking forward to them with the same level of glee as i was the previous ones.
It's possible she's gotten it out of her system now and will want to write more "traditional" books again after this, but on one hand that pretty much flies in the face of the meaning of "closure" (if that's actually what she intended,) and on the other hand, who would be the protagonist of these theoretical future books? Miles, Ivan and Cordelia are all settled down (or re-settled in that last case.) She could switch over to Nikolai, but that would seem a little out of the blue, and it doesn't seem like he's been well set up for a career featuring a lot of adventure. (Though as a jump pilot there's always the possibility for mis-adventure i suppose.) Alternately she could skip ahead 10 or 20 years to focus on the next generation. That has rarely worked especially well in literature, but we're already staring one of the rare counter-examples in the face, so...
But realistically, unless she feels like retiring (she's at the age where that would be reasonable, though by no means required) it seems like it might be best for all concerned if she wrote some more Chalion books instead, or, even better! wrote some standalone books or maybe even started a whole new series!
So anyways, TL;DR (Or just avoiding spoilers):
It's a good book, but you may have an easier time enjoying it if you don't go into it expecting any action or intrigue. It consists entirely of a (well done) exploration and development of some of the characters and their relationships with each other.
And if you start reading the book and are bothered by the apparent out-of-the-blueness of the big "retcon", go read this, it might help: