So I imagine most people won't rate it as highly, but, after reading it almost immediately after it arrived on my laptop, I'm giving this an "outstanding." The story was well-constructed, the dialogue was well-written and true to the characters as they've been presented in canon, the balance among the characters (and between canon and non-canon characters) was ideal for me, and, most importantly, the story made the Nexus more compelling than Generations
did and complemented that movie's story, enhancing both.
Spoilery stuff below:
There are some interesting religious overtones to various elements of the story. Bryant's line about "too intricate to be a naturally occurring phenomenon" contrasted ironically with the self-profession of atheism that immediately preceded it. (For those unaware, the "too complex to be naturally occurring" argument is a favorite among anti-evolution advocates here in the US.)
Anything involving the Kinshaya, of course, is dripping in religious overtones. Not sure there's anything specific/unusual about their appearance here, but I thought they were well-done, and used in appropriate moderation.
There are also some interesting commentaries on the nature of reality and of suffering. I'd have to give it more thought before coming to any conclusions, but I think there are probably some parallels to Buddhist teachings about mindfulness and suffering.
Basically the only thing I didn't like was the reset button at the end; I wish we hadn't had to lose most of the additions to Trek history (however small they may be) that came with this story. But I understand why he made that choice. And it's small quibble in the scheme of things.
In short, The Stuff of Dreams
is solid in its construction, but coalesces into more than the sum of its parts to become an outstanding Trek story. Well done, Mr. Swallow!