This is Vorkosiverse slash fiction and you really need to know your Vorkosigan saga (at least up till Memory) to make sense of this. A Deeper Season is a set of 24 stories of different lengths, but this review is for the story the series is named for, which is the 3rd in the series.
So. How good is it? Well, that depends. Are we comparing it to other fanfic or are we comparing it to Bujold? The story is quite good, actually, no matter what you compare it to, but, as you would expect, it is not quite Bujold. The authors portray a pretty solid Miles and that is better than it sounds, because Miles is a living entity in my head by now and not much can match the brilliance of that creation, except the real thing. So 'pretty solid' is praise. Of course, this is Miles post-Admiral-Naismith, so he's a little more subdued anyway.
The story is slow to start and it really took me some time to wrap my head around a Miles/Gregor pairing. Living entity and all that. As the story progresses that becomes more believable, though. Gregor has a forceful enough personality to match Miles' (unlike the 'wet blanket' (thanks Kate) Miles ends up with in the real story), he's not easily manipulated, not even by the master manipulator, and at the same time he is a quiet grounding force for Miles' momentum. The end of the story has some nice Milesian chase scenes, and it all ends on a satisfying note. If the characters don't shine quite
as brightly as they do in the original works, well, that's understandable and, for me at least, acceptable, just to get to read some more Miles. Yes, I have a crush on Miles. Bite me.
What I found interesting is that this story is about baby-making. Mrs Bujold has a high regard for baby-making in her stories. I don't think she's averse to different sexualities at all (see Ethan of Athos, Donna/Dono and Aral's bisexuality), but since baby-making is so important, we end up with solid heterosexual pairings all the time. And the story plays out on backwards Barrayar, of course, where women can't even inherit. So, on the one hand, it made it feel more like real Bujold that the plot for this story was also driven by baby-making. On the other hand, it might have been nice to lose that particular author hang up.
Anyway, well worth reading. I'll be continuing on with the rest of this fanfic series. Maybe I can make them last until the Ivan book Captain Vorpatril's Alliance comes out. Yeah, probably not.