What things in general have been brought with time into the Eastern Orthodox Church that the main stream protestant Christianity considers as not being able to be traced back to the times of the church of the first century?
Separation of layperson from clergy would be a big one in my book, and for that matter formal recognition of sainthood. To many protestants, if you're not a saint you're not a christian, because all christians have been sanctified by the blood of Jesus. The two states are inseparable. Part of this would be that most protestants also reject the divinity of Mary.