I read Declare and The Jennifer Morgue a few months ago, due to responses to my post about The Atrocity Archives.
First, I was expecting Declare to inhabit the same intersection of genres as the others — hackers plus Cthulhu plus spies. I was mistaken. It is a supernatural spy novel, but there are no hackers and it is not set in an obviously Lovecraftian world.
One funny thing is that some characters appear in both books. Since I’m largely ignorant of British spy history, I wasn’t aware that these were real figures. That’s too bad, I think that sort of knowledge makes the books a bit richer.
The Jennifer Morgue has a great name and is a typically fast-paced Stross book. However, I generally dislike books that go meta, and the whole geas thing was too cutesy for me. I finished this book mostly out of stubbornness,. Also, I find that the frenetic style of Stross or MacLeod wears on me after a while.
Declare was a much different book — slower paced, more detailed, with more history and character development. It was a bit repetitive at times and perhaps a bit long; but I thought the ending was rather clever and I enjoyed it overall. For some reason the title Declare has stuck with me and I think of it often.