Are there any specials? Or maybe usual services (e.g Vespers) are more frequent? I wonder also how is it in OO Churches
As for EO, know that there is a Greek tradition of forty Liturgies, an Advent Paraklesis in the Antiochian Church, and that in some parishes during the week it's sung “alleluia” instead of “God is the Lord” (in the same way as it's done in Great Lent). I wonder if any of these services/liturgical changes are common?
As for OO, I know of course about Kiahk in Coptic church (Kiahk praises). And I know that in Syriac Orthodox Church each Sunday of Advent has special name and hymns.
I can say that in Polish Orthodox Church there is only one thing special: “goveniya” (or “rekolekcje”) – 2 or 3 days of spiritual teachings given by one priest (can be from the parish, but also a guest) plus confessions done during the All-Night Vigil plus penance and before Eucharist prayers that on the last day of “rekolekcje” most of people go to the Holy Communion.
If I'm not mistaken, something like that exists also among Ukrainians (I know at least Ukrainian Greek Catholic Church does it)?
And of course, since the feast of the Entrance of the Theotokos, katabasias of the Nativity Canon are chanted constantly