I voted depends, because I consider traditional Christianity Tri-theistic at least, and a version of polytheism with the OT and the NT depicting a hierarchy of Gods, even a rebel God Satan. This polytheism includes a female God Mary a descendant of the female Gods of the Old Testament.
The Old Testament describes polytheism evolving to a hierarchy of Gods, and then evolving to Monotheism.
Mary is only a goddess to Christian Wiccans, and she only functions like a goddess in certain sects of post-Fatima Roman Catholic devotional life (though Mary being a goddess would be rank heresy in the Catholic Church, just as in any other Christian church). She is in no way, shape or form a goddess in Eastern Orthodoxy, Oriental Orthodoxy or the Assyrian Church of the East. Also, Satan is a rebellious evil spirit, not a deity.
You may disagree with the Trinity, you may choose to call it tritheism, but the fact remains that the Trinity as defined is strictly monotheistic in nature. For example, in Arab lands, Orthodox Christians (especially the Antiochian Orthodox) say "In the name of the Father, and of the Son, and of the Holy Spirit, one God." The Trinity is a Tri-
unity, not an assembly of three different gods. I would recommend reading the declarations made by the First Council of Nicaea and the First Council of Constantinople for more information on this matter.
Moreover, I don't see how Christianity being polytheistic follows logically from the Israelite religion having started out polytheistic but then slowly phasing into monotheism. That's like saying that Judaism is polytheistic because of the same history.