As with most anthologies, this is a bit of a mixed bunch, but they do at least have a unifying theme: (view spoiler)[Vulcans are telepaths, but nobody else in the Mirror Universe knows about it (hide spoiler)]
Looking at the TV episodes, they all involved at least one character from the "Prime" universe interacting with the Mirror Universe, and that provided a contrast. Since these stories are all set entirely in the Mirror Universe, it poses a problem: you can have a story where all the familiar characters are evil (which is depressing) or you can say that the counterparts are also noble (so there's not much difference from the Prime universe). Some authors handle this better than others: I particularly recommend the stories by PAD and KRAD, but I strongly disliked Friedman's Stargazer
story.(view spoiler)["Nobunaga" by Dave Stern (Enterprise). This isn't quite as bad as "Age of the Empress" (in Glass Empires), but it's pretty pointless. Basically, he woke up and it was all a dream. That's a bit feeble when children do it, and I expect better from a professional writer. In fairness, he included a few hints along the way, but ultimately nothing happened; this story doesn't affect any of the later events (which we've already seen) or offer new insight into them.
"Ill Winds" by Dayton Ward & Kevin Dilmore (pre-TOS/Robert April). This isn't bad, although it suffers from inconsistent characterisation: they start out by portraying April as a merciless leader, then show that he's all warm and squishy on the inside.
"The Greater Good" by Margaret Wander Bonanno (TOS). This is pretty good, and I'm kicking myself for never making the connection between the two things called Tantalus.
"The Black Flag" by James Swallow (Vanguard). Considering that I've only read one Vanguard book, and that was a few years ago, this worked pretty well: I learnt everything that I needed to about the key characters, and I certainly got the impression that it fitted into the grand scheme of events.
"The Traitor" by Michael Jan Friedman (Stargazer). I've never read any of the Stargazer books, but I have read a couple of short stories in anthologies (here and in Tales From the Captain's Table). In both cases, there were several character names thrown in, e.g. Ben Zoma, but there was no equivalent description about who these characters are, so the story fell completely flat. In this case, I wasn't optimistic when I saw the title page, but I did wonder whether I was prejudging it based on the writer. After a few pages, they established that the captain of the ship was actually Guinan: fair enough, that's a nice twist, and it explains why she hadn't been named up until that point. However, the story continued to refer to her as "the captain of the Lakul" after that, which felt quite cumbersome. I assumed that this was a combination of poor writing and poor editing: presumably her identity was only revealed at the end of the story in an earlier draft, but nobody had bothered to update the story after that revelation was moved to an earlier point. It turned out that there was actually a valid reason for this, i.e. it wasn't really Guinan after all, so maybe I would have appreciated this more if I'd given the author the benefit of the doubt. On the other hand, the end of the story meant that there were only two characters I recognised and neither of them actually appeared in this story after all, so it was all just a bunch of ciphers doing inconsequential things.
"The Sacred Chalice" by Rudy Josephs (TNG). This was ok, with versions of Deanna and Lwaxana who were recognisable but different, and a sense that this is all relevant to the wider context of Spock's plan.
"Bitter Fruit" by Susan Wright (Voyager). This was ok, although it's been a while since I read the previous Voyager story and I couldn't quite remember where all the characters had been left. In cases like this, I think that a 1-page recap would be very useful.
"Family Matters" by Keith R.A. DeCandido (Klingon Empire). This was a good story, although the characters don't seem to be particularly different to their Prime counterparts.
"Homecoming" by Peter David (New Frontier). This was excellent, as I'd expect, and the sole reason that I bought the anthology. I think it's set before Star Trek: New Frontier: Turnaround but it's probably better to read it afterwards so that the surprises are more effective. I think this story does a good job of mirroring Nemesis, i.e. showing how two universes that diverged a long time ago can still follow similar paths.
"A Terrible Beauty" by Jim Johnson (DS9). This was interesting but I don't think it would really stand up to a second reading, and it does seem like a situation that could have been avoided if people had just talked to each other.
"Empathy" by Christopher L. Bennett (Titan). I haven't read any of the Titan books, but this worked pretty well on its own merits. My main concern is that I'm not sure how it fits in with "Bitter Fruit", since Tuvok appears in both stories.
"For Want of a Nail" by David Mack (TNG-ish). There's not much to this story, but I might be hard on it because I was hoping for a follow-up on Spock's big plan and we didn't get it. I think I'll need to wait for Star Trek: Rise Like Lions to get that. I'm also curious about whether this has any implications for the Prime universe, following up on the events of Blind Man's Bluff, but I doubt that it was intentional. (hide spoiler)]