This book has some pretty damn cool parts, mostly involving the Lovecraftian, Aztec-style vibe that the otherworldy creatures come from.
Unfortunately, the world-building in the otherworld seems to take over ground the world. When you look at the world of Clive Barker, Edward Lee and Ray Garton, all big splatterpunk authors that share the genre with Jacobs, all of them at least try to ground you before you get to the weird stuff.
I'd enjoy it more if it didn't go for broke as much in terms of insanity within the first 100 pages.