The alternate universe in which the Axis has won World War II just doesn't feel right to its inhabitants. Could it be the prevailing Nazi morales, the new social classification, or is it something altogether deeper?
Several very different characters (presumably demonstrating a wide enough variety of this world's social structure) will interact with each other and undergo radical changes, all in their personal efforts to make sense of their existence.
This 1962 novel gained Philip Dick a Hugo award, which he subsequently used to stop a fight in his garden. Thematically, it includes many of the author's obsessive subjects, like alternate realities, socio-financial positioning, relationships, depression, future Vs. the past (all this is put rather bluntly as to not give too much away), though, admittedly, the characters' use of addictive substances is minimal.
Uncharacteristically, though, the setting is brought on, explained in great detail, and never ceases to be a factor to everything that happens (or fails to) in the story. This is a far cry from most of Philip Dick's books, where the "working environment" is only used to explain the particular characters' behaviours and choices, and then focuses on them. In "The man in the High Castle", the world is described in great detail from beginning to end, and the particular events that led to the Allies' defeat are so plausible and well explained as to give anybody a sudden 'close call' panic attack.
In addittion to the above, the novel's wide range of characters are all very deeply carved by the author's obvious empathic demeanour. This is (I think) the first of Dick's novels featuring a different person's perspective per chapter, and it seems to serve the purpose well, though he never really adopted it as a personal style (the same writing style is demonstrated on "The simulacra", a story with more characters, thicker plot, but somewhat shallower).
I tend to believe it was the actual explanation to the different WWII outcome that the Hugo award was rewarded for in this case, though I find the character development therein the most notable. This is definitely not a typical Philip K. Dick book, but rather his best authoring traits put together. The obvious labour involved in its writing (the historical and cultural research as well as trying to make out and tie together the I-Ching hints that indicated how the story should proceed) eventually paid out by the creation of a true landmark of an uncertain era and one of the first science fiction works to command literary acclaim.