One of the reasons that there are so many compositions in the Russian tradition, is that during the Russian empire, graduate students in music were required to compose a setting for the All-night Vigil and the Liturgy as part of their graduate school program.
There are many styles of compositions, some very operatic and western, others from the so-called "National School" were adaptations of traditional chants.
On another tangent, the Georgian church has an ancient tradition of polyphonic chant that typically uses three voices, which move independently. There are many local chants which are quite unique, such as Kartli-Kakhetian chants and Gurian chants. Georgian church music, like the Georgian language, is unrelated to any other Orthodox musical tradition. The Georgian Cherubic Hymn "Romelni Kerubimta.." is absolutely beautiful and almost hypnotic. The reverence for church singing is shown by the fact that singing in church is described by a different word "Galoba" than the word used for secular or folk singing "Imghere". Lord, let me hear the choirs of Gelati and Sameba again !
There are many great recordings of church music available in Georgia; but not many here. If anyone is interested, I have a few books that have collections of Georgian music in modern notation, that I could xerox and share. If anyone is interested, they can e-mail me at my address.