I have an odd relationship with the Sandman Slim books. I look forward to them, and yet I'm starting to feel as if they're running out of gas. I didn't hesitate to pre-order The Perdition Score, and yet as I began it, I felt that we'd been this way before, too many times. I felt the same way about the last couple of books too.
At about the 25% mark I find myself actively engaged in the story, though, and enjoying it. I love the characters (Stark is actually my least favorite.) and the universe is just mad enough that it remains intriguing. I get to the denouement, and often feel a little cheated, as if there was too much build-up and not quite enough pay-off. But by the end, I'm usually pretty satisfied. Enough so that I know I'm going to read the next one. I believe Kadrey has said that the next book will be the last Sandman Slim, though, and frankly I'm glad. I'm not sure how much more he can wring out of this universe.
As for the particulars, Perdition Score has the usual cast of characters: Stark, Candy (now known as Chihiro) Kasabian, Vidocq and Allegra. The plot revolves around the chaos in Hell now that Lucifer has left. Nearly everyone wants to get into Heaven, but in spite of Mr Munnin's promise, the gates of Heaven remain closed thanks to a war between the angels who want to open Heaven and those who do not. A group of both living and dead magicians known as "Wormwood" are trading in a mysterious substance called "black milk," and when one of Stark's friends is poisoned with it, he is forced to go back to Hell and try to track down the one thing he believes will save his friend.
In the end, though we've been here before, the story is satisfying. It ends on an oddly disturbing note, but I'm assuming that will be resolved in the final novel. And yes, I'll read it. I may have reservations about the series, but now that I know it's a finite one, I'm willing to ride along to the end. Bottom line is that Kadrey has never disappointed me even if I find later books to be a little repetitive.