After quite high expectations, I have to say that Worldsoul turned to be a little mixed for me as the novel aligned closer to the UF subgenre than to the SF that remains by far the most interesting of the author's oeuvre to date. It is true that the novel is not quite the usual UF junk as it takes place in a "higher dimension" from Earth, but Earth's cultures, myths, supernatural beings of lore, books and tales are crucial for all that happens.
Worldsoul has great inventiveness and the writing style is the compelling one I have been expecting from Liz Williams with interesting main characters, and action happening in the higher dimensional city Worldsoul of the title, metropolis which is in a bit of disarray as its former rulers vanished a while ago and the various powers to be have started the struggle for domination.
Mercy is a somewhat naive but dogged librarian - though of course not of a mundane library - from a Northern tundra clan lineage whose two mothers have left on a quest to find the disappeared rulers - Worldsoul is a Liz Williams book so expect men to have minimal roles if they are not dispensed with as in her superb Solar System novels like Banner of Souls or Winterstrike - while Shadow is a devout alchemist from a Middle Eastern inspired culture who is compelled by the local power broker, a male Shah, to do some work for him that her ethics code finds distasteful.
A few demons including a duke of Hell - still female - who is the best and funniest secondary character, Disir i.e. Loki's supernatural minions, and assorted supernatural beings play the humans and one another and are occasionally played in turn while the novel moves at a brisk pace and ends at quite a satisfying point solving its main local stories though of course the big picture is just coming into focus as the ending emphatically punctuates that.
Where my reservations lie is in that the whole UF setup is a bit hard to take seriously and the external world lacks focus with the Worldsoul itself more of an abstraction or a stage if you want for our characters than a "real place" with texture and depth.
On many occasions scenes that are supposed to have tension simply lacked it for me as I had no idea what the parameters were (and no idea if the book follows standard UF ones as I heartily detest the subgenre) so the various fights, chases etc read: "well this happened because it happened" with no way for me to realize if it was normal, an act of valor or something unusual.
I would compare my experience in those parts of the novel as with reading about a Wild West gunfight without having any ideas what guns can or cannot do - pretty much everything described can happen as the fact that the sheriff is faster on the draw may simply be so because his gun is a "lawful" one so it comes out faster, the fact that he shoots straight and the villain shoots badly maybe because his gun is an AI that targets himself etc and if the author inserts that the sheriff's gun shot 500 times in succession without recharge, it may seem a little odd but hey, it may be possible after all...
Overall, I think that if you are a UF buff you may love Worldsoul a lot, while personally I found it entertaining and I would definitely recommend it. Not as grand as the author's excellent sf, but I am still looking forward to see what comes next in the series!
Note: This review has originally been posted on Fantasy Book Critic and all links and references are to be found there