So this guy comes back from Hell bent on revenge, the way one finds oneself doing, for the brutal killing of his girlfriend. He was sent, still living, into hell and ended up fighting in the gladiatorial arena down there to stay alive. So he's pretty much awesome at killing things, and before being sent down he was an incredibly gifted magician (both of which equip him solidly for his chosen career path (Mayhem Application Engineer)). So anyway, he comes back to revenge himself on the people who sent him to Hell and who murdered his girlfriend.
The problem with Sandman Slim is that the main character, by dint of living in Hell for seven years or just natural inclination, is an unrepentant asshole. He isn't a very sympathetic character, and it's hard to really care all that much about his suffering and whatnot because he's largely an emotionless revenge machine. That sort of thing *sounds* really badass on paper (especially if that paper is a character sheet, I've found) but it makes it hard to become emotionally involved with his story. He moves through a world filled with interesting characters, cool magic ideas, horrible creatures, awesome cosmology and all that sort of urban fantasy stuff, and it is all very cool! The friends he makes *are* quite interesting and sympathetic, but they are very marginalized and rarely get any screen time and don't get to develop at all... the same could be said about all of the cool elements. Kadrey just seems to neglect the parts of the book that were interesting and stay tightly focused on a protagonist that doesn't draw the reader in.
Then there's the revenge bits: these were all... weird. None of his victories felt like triumphs, perhaps because it never seemed like it was any effort or risk to him. I'm not sure how to describe a revenge fantasy novel in which the various revenges aren't actually cathartic at all. Firstly because you don't care all that much about the wrongs that were done to this guy, and secondly because the obstacles seem trivial and he walks through the actual revenges like he's out getting groceries.
All this sounds pretty negative, and I guess it is. I didn't *hate* the book but I don't feel like I got anything out of it either. There were lots of very, very cool ideas that could have been fleshed out into fascinating aspects of the story and I dearly wish they had been. Give me a scene of the arena fights! Show the immortal alchemist more! Play with the punk rock girl spider person more! Instead, I found that the most singularly positive thing about the book is that it's form factor is totally awesome, if you're into kinda weird sized printings. Which I am. So there's that.
Otherwise? Pass probably.