I picked up Van Richten's Guide to Ravenloft and have been reading it cover to cover. This is my review of the book, chapter by chapter. The first part of chapter 3 covered 17 domains or so, and this second part dedicates two paragraphs to each one of the other ones. Having read through the featured domains, I think it's probably a good call. The "domains" in this section are really just thoroughly entertaining and inspiring story seeds you could use almost anywhere within Ravenloft. A headless rider, evil toys, a ghost dancer, a shapeshifter who must feed on flesh, a hounted lighthouse, a supernatural detective agency that's been drained of all colour, and much more. Every single entry, a mere two paragraphs though they may be, are brimming with story ideas.
By this point in the book, you know Ravenloft well enough. You don't need pages and pages of travel guide tours of each domain. No matter what the origin of the story, you can guess that the domain is spooky and macabre. It's Ravenloft. The real value here are the stories.
It does make you wonder, though, why the domains are necessary at all. Why not just have a setting that contains all of the macabre locations? I love reading about Ravenloft, but even with the featured domains I sometimes struggled to find what was unique among some of them.
In Pathfinder, Golarion is essentially a catch-all setting. When you want gothic horror, you go to the gothic horror regions. When you want high fantasy, you go to the high fantasy regions. That's how Ravenloft is in the material about the domains of dread in old 3.5 source books. Back then, Ravenloft was a proper campaign setting rather than just a location in the Shadow Plane. The old domains, although separated by mist, had interactions and relationships and politics, and mercantilism and trade routes, and even espionage.
But the 5e domains are more or less self-contained, unless you happen to have a domain talisman to find your way from one to another. I'm not sure what the benefit of this design is, and I feel like 5e Ravenloft would make more sense to me as a contiguous setting instead.
The 5e domains of dread are small worlds with essentially one major theme and plot each, and so the lore for each can, and arguably should be, brief.
For me, Ravenloft is stronger as a setting than as a location in the Shadow Plane. I'm a fan of lore, and part of the satisfaction you get when you're a fan of lore is answers. Things get explained through lore. Sometimes they're things that define the setting, and other times they're trivialities that will probably never be mentioned in any game. It's not the significance of the information, it's that the lore exists.
Ravenloft in the Shadow Plane is confusing. Are the people in a domain of dread soulless reflections of real-world people? Or are they brand new beings created for Ravenloft, with fake memories to make them seem real? Or are they real-world people who were whisked away as collateral damage of being physically near the darklord?
What are the people's futures like? The book says that the year in the domains of dread is always 758, and yet Baron Kharkov got supplanted by Chakuna, and Azalin Rex has apparently escaped from his domain. The book suggested that domains are caught in perpetual cycles for the benefit of its darklord, so what happens when the darklord is gone?
And what about the land and structures within the domain? Do entire regions go missing off the face of their planet? And if so, why is the origin planet almost never specified, as if the domain existed in Ravenloft all along? The answer, obviously, is that the domains did exist in Ravenloft all along, since way back in 1983, and it often feels like this book didn't know itself that Ravenloft wasn't a stand-alone setting until the last minute.
In the end, I'm finding that the correct answer is a lot of hand waving, ending with a shrug and a casual "Who knows? It's Ravenloft!"
I'm OK with that, honestly. It's nominally better than the Gap of Starfinder, because at least the new Ravenloft isn't supposed to exist in the real, rational world. While the Dark Powers in 3.5 mainly controlled the mists to define the boundaries of domains, in 5e they're great all-powerful scapegoats. When something makes no sense, and there's no lore to explain it, blame the Dark Powers.
Most of the other domains read a lot more like subplots for the featured domains. Personally, I'd have probably just put most of them in corners of the featured domains. Forlorn, for instance, could be a little duchy within Barovia. Keening could be a subdivision within Mordent. And so on.
However, I personally don't have to consider the thousands and thousands of players who know and love these domains and definitely want to see each one at least mentioned in the definitive book on 5e Ravenloft. Considering it that way, you have to wonder whether it's enough that any of the domains only got six pages at the most and 2 or 3 paragraphs at the worst. But I think the 5e principle has been to summarise and condense, relying on old source books as added reference material. You want Secrets of the Dread Domains for additional information on the darklords and former darklords? No problem. Thanks to Dungeon Master's Guild, most everyone who really wants the lore has access to it at least as a PDF and sometimes even as a print-on-demand hardcopy.
In my mind, the Magic the Gathering Innistrad and Amonkhet settings are domains of dread. This is largely an arbitrary declaration. There's no reason for them to be domains of dread, but they both have Planeshift editions that, frankly, read a lot like the quick summaries in this book. A little lore, an overview of key characters and plots, and guidance on how to re-skin existing stats instead of new monsters or stat blocks.
Until we get full setting books for them, like Ravnica and Theros and Strixhaven, Innistrad and Amonkhet are just visible through the mists from Barovia and Har'akir, respectively.
The next and final section of chapter 3 is Traveler's of the Mists, which is all about the brave souls who traverse the domains of dread.