I read it and never got why its s'posed to be so good. I've read better alt history stories.
The mistake is that you approached it as an alternate history.
High Castle has the superficial trappings of an alt-history, but that's not PKD's
point. He doesn't care whether or not his alt-history is plausible, because it's not. He's more concerned with what do people do when they live in an insane, unreal world? It's a familiar theme in his work; the world feels
wrong, and the characters confront the
wrongness of the world, until they peek through the barriers and see the way things
should be. In some books (
Time Out of Joint, which
The Truman Show borrowed heavily from), the perceived world is largely artificial. In other books (
The Three Stigmata), the real world can be accessed through drugs. In
High Castle, the real world can be accessed through the
I Ching, which reveals the truth of the world's unreality. This is why the ending of the book is so unsatisfying on first read; even the knowledge that the world is wrong doesn't effect a change, because it
can't. Just being able to see the bars of the Black Iron Prison (a term that won't show up in PKD's work for another decade) doesn't
remove the bars. The unreality is still real.