I didn't even know this was a thing, but I definitely felt like Diamond Age just sort of ended mid-sentence. It's got all the elements of a great ending. I suspect it's something in the cadence, like if a symphony just ended with a V-I "BUMP DUMP!" without any sense of "everything is resolving into a tight knot." Instead, he lays out all the thread, everything is there, and there's just not really any way to wrap it up without being trite.

For an author with a similar style who does do endings, I'd say look at Heinlein. But this is all kind of besides the point, because Young Lady's Primer was basically my favorite book at the time I read it, and is still in the top of my personal charts. Sure, it doesn't have an ending or even a coda, but it just doesn't matter, because the mass of thread is beautiful without being tightened or tied off.

What is the point of the book? It's a fascinating world he created, but all the action is about nothing. It's so inconsequential compared to everything else going on. The problem starts way before the ending. See my comment about MacGuffins elsewhere in this discussion.

You can write off swaths of books and entire genres by asking "what is the point" but that aside even if someone offered an answer would it change the way you feel about it? No.

I'm fine if a story doesn't have a point, or if it leaves things unresolved. The problem with Stephenson (for me) is that the book is written as if it is leading to some shattering conclusion, and then it just doesn't. It fizzles right at the point that you are about to discover the long (because it's Stephenson) sought resolution.

I would have preferred the Diamond Age if it just was about that world, but without all the kerfuffle about the big secret. Nell wanders off into the sunset, or whatever.

Novels with a meandering world-building focus (e.g. LotR) are like a polar opposite and the most boring genre fiction in existence.

> as if it is leading to some shattering conclusion, and then it just doesn't

This sounds like another way of saying the story was fast-paced and engaging, and you didn't find the conclusion to feel like a "climax" with explosions. That's ok (notwithstanding that there was a big fight and all), but I think in "idea-driven" books like this it's just as well to leave things ending either strangely / unexpectedly, slightly unresolved or whatever. It's hard to put a bow on a story that can't really have a happy ending. Weird stories should have weird endings.