A supernatural spy thriller from Charlie Stross ought to be entertaining, but this is Tim Powers country, and Declare covered this ground much more effectively. I’d hoped that the humorous IT angle would work, but it doesn’t; Stross doesn’t let his bureaucrats really be bureaucrats. Saved from mediocrity by one remarkably effective set piece.
If I recall correctly, Stross agrees with your assessment of the relative merits of Declare in an afterword to The Atrocity Archives, where he also says that the similarity between the two novels was fortuitous.
What was the set piece that you liked?
The mounting sense of dread as they go through the portal is very effective. Nothing really happens for about a chapter, but they keep discovering more and more things that are somehow off. (I’d also note that this is a chapter in which two of the three genres more or less stand back and let the third do its thing.)