It's a western religion because it is descended from the God of Abraham and because it recognizes Jesus as a prophet.
It is a rather great heresy, but no more so than Christian Science or LDS. It is rather belligerent, but it has conquered no more territory than Christianity.
It strikes me as medieval, but then what we call medieval was Christianity before secular governments arose.
"It strikes me as medieval, but then what we call medieval was Christianity before secular governments arose."
"Secular" only in the sense that the government was actually a separate entity. And, this didn't just arise, whole, out of some primordial soup ... it was the direct result of the Protestant Reformation.
From the viewpoint of the Greeks at the time of Alexander (which is the classical standard of Western civilization), all "western religions" are what they would have considered eastern. It's only because Rome abandoned its traditional gods and became Christian (300 years after Alexander) that we consider the Abrahamic religions to be part of the West. Originally they weren't.