I suspect Rooms' rating has suffered for two reasons. One, there are virtually no likable characters. Everyone--including the ghosts--is alcoholic/depressed/insecure/lonely/pick-a-page-from-DSM-5.
Two, there's not much resolution. A few secrets come to light, but the characters for the most part aren't illuminated with shattering insights and new leases on life.
(For my part, I liked the ending. It affirmed my belief that personal change is generally painstaking and incremental. Had there been an epidemic of life-altering epiphanies I'd have been disgusted.)
Rooms reminds me strongly of The Casual Vacancy, which is a good thing. It's all about relationships and secrets and unhappiness and how we edit our memories to fit our narratives, and to rationalize our grudges and hatreds. It's not as well-written or epic as TCV but it shares themes and tone, and it's similarly brave in it's willingness to go dark.
The numerous "rooms" metaphors are often clumsy and forced--rooms are like secrets, and people, and chapter titles, and memories, and I forget what else--but they don't interfere with the plot so I found that particular clumsiness easy to set aside.
If I try to do my usual summary/analysis thing I'll be here all day. Suffice to say it's brutal, long, heavy and glorious. And occasionally sickening.
First, I gotta say that The Ultra Thin Man needed a much better editor. There were far too many typos and jarring disconnects:
"On the facing page was a photo of five scientists: two humans, a Helk, and a Memor." (See, I require that my science fiction authors be able to count to at least five. Bare minimum.)
"It can't have been an antimatter weapon, the amount of antimatter needed has never been created. Also, the rays from the antimatter weapon that I just established doesn't exist are going to kill all the living things still on the planet." (o_O)
After 120 pages of discussing First-, Second-, and Third-Clan Helks (varieties of aliens), I suddenly encountered some Second-CLASS Helks. Oops. And there were plenty of other examples.
Then there were the logic gaps and motive failures. Why are the bad guys constantly capturing people, detailing their evil master plans, and then leaving them alive to escape and save the day? "Bwahahaha! Now that you know everything, I think I'll kill you later." How do you disappear several tens of thousands of law-abiding citizens and no one in eight worlds seems to wonder where they are? Why are there no rescue missions to a dying world when it's only six hours away by press shuttle?? Ye gods, you could drive a truck through some of the plot holes.
So why three stars? Swenson excels at setting a hook. Probably three chapters out of four ended with a cliffhanger so good that I couldn't stop reading. That's it. Even when I was rolling my eyes I had a hard time putting it down. I don't have much respect for The Ultra Thin Man, but I did have fun reading it.