This book is the worst thing I've read in quite a long time. The story is told in a series of episodes (Feels like it may have originally been published in a magazine or something?) in which the nefarious rat-man Skaven try various plots to invade the generic fantasy city of Nuln and are repelled with minimal effort.
I'm told that the heroes are more fun if you read the first book in the series, and I admit, I haven't. Gotrek is a disgraced dwarf who wants to redeem himself with a noble death in combat, but can't, because he's too good at fighting. In fact, almost every conflict in the book is resolved by Gotrek easily showing up at the right place at the right time and killing all of the bad guys without breaking a sweat. His personality mostly comes through in generic one-liners like "let's get kiling."
Meanwhile, his sidekick, and the typical viewpoint character, is Felix. Born into a wealthy merchant family, he's left a guaranteed cushy lifestyle of wealth for adventure. Felix is the blandest character imaginable, and about half the ink in the book is wasted on his banal thought process. Felix gets a letter? We get three paragraphs of him mentally listing all the characters who might want to write him before he bothers to read the return address. Felix decides to buy something in a shop? Get ready for two pages of him looking at every other item in the shop first and deciding not to buy them one-by-one. It seems like every time King wrote a chapter, he came up a few thousand words short, and padded his wordcount with constant dips into Felix's tedious stream of consciousness. This book builds "mystery" by letting Felix speculate ten possible outcomes to every decision he makes before telling you what happens. Felix also has a perfunctory romance plot in this novel, which is a constant source of anxious walls of text for him, and not much else.
The Skaven are backstabbing, selfish, factional, power-hungry manipulators, and what little fun there is to be had in this novel is in seeing their general, Grey Seer Thanquil, habitually rationalize his own duplicity and cowardice while scheming against his political rivals for the exact same traits. In the hands of a better writer, this could have been a blast, but the best scheme he can come up with under William King's pen is to send letters to our flavorless protagonists once per episode, tipping them off to his rivals' invasion plots so that they can foil them again and again without needing to do anything but sluggishly react. The Skaven never feel like anything close to a credible threat to our heroes. Between curbstomp battles between Gotrek and the rat-monster of the week, King makes an effort to describe the Skaven's plots' effect on city's population, but none of it carries the least bit of weight, because nothing bad ever happens to any character who anyone could possibly care about.
Most of the Skaven characters seem to exist for promotional reasons. This book seems to be intended mostly to get the reader interested in playing as the Skaven in the Warhammer Fantasy game by showcasing all the different character units. There's a clan of ninja rats, a clan of rats who spread disease, a clan of steampunk tinkerer rats, and a clan of rat Dr. Frankensteins, who breed different kinds of non-anthropomorphic rats as biological weapons. We also see giant rat-ogres highlighted. At times, Skavenslayer feels like an extended commercial for a Warhammer expansion, like a G.I. Joe episode featuring all the new G.I. Joe toys. Each unit gets a loving look at its special abilities and flavor text before Gotrek steamrolls it and we move on to the next one.
I don't know who I could recommend this to. Even if you're obsessively interested in Warhammer lore, the Skaven in your imagination at your game table are almost certainly more interesting than this.