Impossible Landscapes is beautiful and engrossing. I have no particular interest in the Carcosa/ King in Yellow mythos. I expected to just skim it for ideas. It sucked me in so fast that 19 pages in, I found myself making a red string board of the connections it was hinting at in the images and marginalia.

I can sincerely say this is the most beautiful book I've ever read; and the art doesn't get in the way of function. I've never read an RPG with better layout. It's easy to navigate the main text and sidebars to understand how to run the campaign. It's also easy to see how to weave setpieces or characters from Impossible Landscapes into an existing Delta Green game. And if you want, you can go very deep extracting extra ideas from its marginalia. (Snippets from Project Stargate documents and Wikileaks releases; anagrams like "Hygromanteia = Mahogany Rite"; hints at the Imperial Dynasty of America timeline...)

There are two flaws, both common in horror campaigns:

1) There are setpieces that players will think can be solved by investigation or combat, but actually can only be solved by fleeing. (Don't make your PCs wander around losing sanity while learning nothing until everyone's bored and frustrated; or all get anticlimactically shot dead without knowing why or by who. Drop appropriate hints).

2) The book gives the GM a ton of cool information, much of which the PCs have no way to learn and no reason to investigate. (Come up with ways for your PCs to discover everything in the book that strikes you as particularly interesting, horrifying, etc).

These flaws are less pronounced than in some older Delta Green books. The authors are clearly aware that stubborn players will try to find the end of an endless maze or stand their ground against respawning murderers, and aren't cheering for the GM to trick their players into failure states. There's appropriate advice on how to run a horror game, how to keep players' choices and their characters' defining traits important within an overall mood of doom and danger.

Impossible Landscapes is a joy to read. I'd love to run the campaign. I'd recommend reading it for the story and art to anyone with an interest in horror, alternate history, or investigation.