It's pretty failtastic. I mean, like
lady_ganesh said, it's hard to catch among the flying plot and tons of world-building, but once you realize it you see Carey set up a society of Jewish cultural markers, and an archtypical Friendly Rabbi Advisor. But these bearded, black-coat wearing people point to the death of Jesus as their genesis, not the three thousand odd years of history before that.
One of the problems is, in order to analyze the divergence between Judaism and early Christianity, you have to treat Christianity as myth and Jesus as a construct. Jewish theology typically treats Jesus as a false prophet, when he's addressed at all. Starting from the premise that the Christian mythology is factually correct
precludes the Jewish tradition that Jesus was an upstart who wanted to be king, and accedes to the Christian tradition, that maintains that Judaism was theologically acceptable up until Jesus, but once it diverges from Christianity it becomes heresy for refusing to acknowledge the divinity of Christ.
The idea of "Judeo-Christianity" is an interesting social construct, but it creates the impression that Judaism and Christianity have a lot more in common than they actually do. It belies the fact that Jewish and Christian theologies are mutually exclusive; one has to be wrong for the other to be right, and it's the one that encompasses the majority of the Western world that usually wins out, unsurprisingly.