The last sentence of the English summary says this is a cheerful adventure story.  This is a blatant fucking lie.  On the one hand, the main relationship between Kou Tong and Huang Jinchen is, for the most part, straight forward.  They meet, they get on like a house on fire, they flirt, and then they fall in love.  This is the lightest part of this novel and the main story is focused on an inception-like psychological tool that malfunctions and drags in 7 unrelated individuals, creating a world where they each get what they desire most but this all depends on a fragile balance as one of them being removed can destroy the whole world and have unknown but likely deadly consequences for the rest of them.
Kou Tong and Huang Jinchen try to gather together as many of the subjects (I really want to say dreamers because a lot of the concept of the Projector reminded me of Inception) as they can to help with balancing their mental happiness but they can't bring over everyone and it turns into a sort of conflict with one of the subjects, a young girl with paranoia and delusions who has found herself in a world that complete validates her delusions and she sees them as intruders trying to destroy her kingdom.
Over the course of roughly 10 days, they build a small, happy little family group while trying to get back out which only makes this all the more devastatingly sad because not everyone wants to leave and this is absolutely not going to end happily for all of them.
While this story does touch a lot on themes that Priest likes to explore in their novels, the main focus on this one seems to be how life is not always fair and that you can't always help everyone.  Most of these people have heavy psychological burdens that affect them in a lot of ways (the paranoid/delusional girl, an abused child who can't speak, a teenager with extreme depression and self-harm/suicidal tendencies, a man buckling under societal pressure, an old man literally on the brink of death, and then Kou Tong and Huang Jinchen themselves, the former of whom lost his mother at a very young age and the reason why is heartbreaking, and the latter of whom was raised pretty much since birth and genetically modified to be an almost inhumanly talented assassin) and they each get a perfect resolution to their problems in this fake world.  It makes it very hard for some of them to be willing to give it up.
It's a good story but definitely a tragic ending for some of the characters.

Why not 5 stars?
I couldn't believe how quickly this story was flying by in general and some things I felt did suffer a lot so others could shine.  Specifically Huang Jinchen.  I really enjoyed him as a character and I was kind of looking forward to a deeper dive into his own psychology, especially since it was clear from the beginning of the story that while he could fake a relatively normal personality, his inner monologue showed he had extreme difficulties seeing other people as anything other than targets and especially looked down on people he regarded as "weak" because he didn't understand how they could possibly continue to survive. 

Unfortunately, he's the only one in this fake world that doesn't actually seem to have anything that he wants.  For example, for Kou Tong, he gets his mother back.  Yes, she's just an idealized projection of the woman he remembers from his childhood, but she's still there.  For the abused girl who couldn't speak, she can communicate with everyone telepathically.  For the teenager, he finds a purpose and a use within the group that fills him with validation and fulfillment.  For the man buckling under pressure, his family, the biggest burden he has, is gone, along with all of his other troubles.  The dying old man gets a whole dimensional space of his own, keeping him alive and at his most peaceful moments.
But for Huang Jinchen there was... nothing that I could pinpoint.  If anything, it was simply that he fell in love with Kou Tong and Kou Tong returned his affections super easily.  It's possibly the most straightforward relationship I've read in any Priest novel but that also made it weak developmentally, especially when it seems that most of Huang Jinchen hinges on either doting flirt or psychopathic murderer.
Also they have the whole thing with both Huang Jinchen and Kou Tong having been genetically modified and experimented on by Seed but they don't really... do anything with it.  I'm not sure if this is because I didn't read the other novel but that seemed to be more about Utopia.  Seed is just something thrown in there for flavor and who the fuck even knows what happened to it after they left.  Are kids still being taken and genetically modified?  I have no idea and it doesn't seem like they do either or that they even care.