This is a tremendously fascinating book, the marriage of noir detective fiction and a historical what-if.1 The book takes awhile to get going, but eventually takes off and introduces a slew of fascinating characters and plot hooks.
To me the most interesting character plays a minor role in the opening third of the book: Zimbalist or the “boundary maven.” He is responsible for running out the string that maintains the eruv, which holds together the border of a home, allowing residents of an orthodox-Jewish island to consider the entire island a single residence and go about their business without breaking the Sabbath. Chabon likens this to running a scam against God. More ironic is that Zimbalist himself is not considered to be that holy a man, but he has tremendous power over the crime lords that run large parts of Sitka.
Chabon also has some interesting commentary on the American government, which is purposefully propping up a organized crime syndicate in order to bring in the Messianic era. The US government is aiming to bring in the end times and helping to cover up a number of crimes in order to do it. The alliance between evangelical Christians and the far-right Orthodox Jews both in the US and abroad is an important part of contemporary US politics and there is interesting commentary on it here.
1. Turns out that the Alaskan resettlement plan was entirely real!