Orthodox Christian here. Crappy one a lot of the time, but nonetheless.
The Orthodox Church and Catholic church split over various things in the 900s. Basically, the Orthodox Church hasn't changed much since then, whereas the Catholic Church likes to constantly evolve to suit the times. I don't know, there's enough to write a few 10 page essays about the differences between the Roman Catholic Church and the Eastern Orthodox Churches, so yeah.
As far as my personal reasons, well, I was raised in a Fundamental Baptist household, so really strict legalistic horribleness there. Pastor would preach sermons about how you can't go to the movies ever because you'd be like part of "the world" and stuff. So after 6th grade, stopping going to church entirely. Was I guess Christian but like, more agnostic at that point, and then some bad stuff happened in my life and I got back to church.
The church I went to started from my highschool's Christian club, and it was one of those "emergent" churches, very much more leaning toward the Pentecostal/Charismatic end of Christianity. It was really neat at first, as suddenly I had a lot of "friends" and liked the whole like, community togetherness thing, but this place was the place that made me realize the reality of my NVLD diagnosis, and that I was different from others. Basically, the church model was like "hanging out" in the name of God, and...I couldn't get it to work.
So after a bit of crisis with a lot of beliefs, I finally just sorta settled on the Orthodox Church as being closest to what I believe in theologically. That, and it gives me a solid base of theology, so to speak, to work from, rather than being tossed about ideologically all the time. The other thing, too, the Orthodox Church is I think much more appreciative of "nerdy" types. Lot I can say, but yeah.