Alternate history as a sub-genre often gets a bit consumed with its own cleverness, but The Man in the High Castle takes quite a different approach. The plot, as far as it matters, is about two German plots, one to attack Japan, the other to assassinate the author of a novel where Germany and Japan lost the war, and the attempts of Japanese and Americans (and one dissident German) to thwart them. Dick almost instructs us in how to read his alternate history, by having his characters read and talk about their alternate history, and with other incidents probing the links between reality and authenticity. There are a couple of "normal" Dickian moments, when one character somehow finds himself in our world, and when others discover that their world is also fictional; but the flaws in reality are much more subtly done here than in many of Dick's books, and for that reason more effective.
It is a peculiarly subdued novel. Dick's writing is often manic: this isn't, except perhaps just a little towards the end of Juliana's journey. She and Frank never get back together. Mr Tagomi triumphs morally but is damaged physically. The man in the high castle actually lives in a fairly normal house and isn't really very nice. But it lingers in the memory.