I know there are a lot of positive previous reviews, but I'm going to play the devil's advocate here. Slasher isn't necessarily a bad source book, but it may not be worth it to actually buy it unless you plan to have serial killers play a prominent and continuous role in your stories. Frankly, even if you are, the amount of brain-storming fuel it supplies is limited at best. You could just watch a bunch of serial killer-based horror movies and pretty much get the same result. And that's my main problem with Slasher: WoD is normall very inventive, but in this case I don't think they did enough with the Slasher medium. I think half the reason for this is that once you start reading it you realize the book is blatantly a supplementary piece for Hunter: the Vigil. If WoD had not been so focused on attaching Slasher to the Hunter genre, they probably would have given themselves more wiggle room. For instance, with a few exceptions ALL of the slasher types presented in this book are HUMAN. We are not given a sample of what a vampire, werewolf, or mage would become if they went down the Slasher path. We are also never given a look at Slashers through the perspective of these beings. Instead, all Slashers presented, with the exception of a few ghosts and immortal (but not vampiric) beings, are either humans or "fallen" Hunters. And the slashers within are viewed entirely through the perspective of humans and Hunters.
Slasher is crammed with a lot of unnecessary information about organizations like VALKYRIE and VASCU, despite the fact that the book itself points out that both of these organizations rarely pay much attention to Slasher activity. If so, why were they put in this particular book? Granted, they provide aggravating new antagonists for werewolves, mages, and vampires, especially since not only are both of these organizations government funded, they were also specifically formed to go after supernatural beings. I just don't see why they were put in Slasher and not some other book (perhaps a new Night Horrors book focusing on human antagonists) where their presence would have made more sense. As it is, we get a massive information dump about the background, powers, and advantages of VASCU agents, which takes us away from the topic of the serial killers altogether. Slasher also assumes that the reader knows a LOT about Hunter: the Vigil, specifically the various Hunter organizations. Frankly I think the front of the book should have had Hunter: the Vigil stamped on the bottom, because this is clearly a supplementary book for that genre.
All in all, I found Slasher to be a disappointing buy. I'm primarily a storyteller/player for Werewolf games, and I managed to glean a rather limited amount of story ideas from Slasher. The only one that even slightly made the book worth the price I paid for it was for the Bone Shadows in the Lodge of Death to hold a grisly "Scavenger Hunt" for their members wherein they reward whoever can kill the most serial killers within the span of a month with a Lodge-specific Fetish, the Ghost Stake. This competition not only requires the participants to go far afield from their territories in search of prey, they must also avoid scrutiny by human authorities, and meddling by human Hunters who just don't understand that not all supernatural creatures are evil. And even after all those hurdles have been cleared, there's the matter of the serial killers themselves, some of which might have inexplicable supernatural powers of their own. Granted, this is a very interesting and engaging story idea, but it's just ONE. After this story is through, your players will likely have had their fill of serial killer antagonists. You could avoid this by having one serial killer per story instead of having multitudes of them in a single one, but no matter how you slice it, eventually your players are going to get sick of having serial killers thrown at them. The use of this book is quite limited, so you should really consider before you buy it whether your money might be better spent on a book you can get more out of.