As an aside, I don't know many Greek Orthodox people who regularly practice. I know a lot of Greeks that claim to be orthodox, but they're really more of a "go to church on Easter and Christmas" type.
I know a lot more Ukrainians, who belong to some variation of the Eastern Orthodox church; and Russians who are, of course, Russian Orthodox. I also know several Egyptians who are Coptic Orthodox.
My own experience with the Eastern Orthodox Church is that it's much more liturgical than either Catholic or Protestant religious practices. Chants, in particular, seem to take precedence over sermons. And they do things like recite the Nicene Creed, as opposed to the Apostles' Creed or something along those lines.
From a theological perspective as well, it seems to me that Catholics place a perverse level of emphasis on Mary. Which the Orthodox church rejects, with a wholly different theory of original sin more properly mirroring the Protestant denominations.
Whereas Catholics will even pray to Mary as if she were some kind of intercessor between mankind and God, Orthodox churches engage in no such nonsense.
Likewise, whereas Catholics emphasize the agony and suffering of Christ on the Cross, the Orthodox church seems to correctly place emphasis on the resurrection, Christ's triumph over death and the prospect of eternal life in the Kingdom of Heaven.
Finally, whereas Catholics seem to place a lot of emphasis on the celibacy of priests, which invites all kinds of problems. Orthodox priests can marry, and are encouraged to do so. This, to me, makes the most sense. The rule of celibacy seems absurd to me. And I see no evidence in the scripture supporting it.
I know there are differences in transubstantiation as well, and communion as a practice. But I think the Orthodox tradition (everyone takes communion) makes more sense than the Catholic tradition (only after confirmation). The leavened vs. unleavened bread seems stupid to me, and leavened bread was that originally used by the Orthodox and the earliest churches that predate the Catholic church by hundreds of years.
Other differences I'm aware of relate to the role of icons, saints and the like. Catholics pray to saints. Not sure if Orthodox do or not, but the practice of praying to saints is something I do not approve of ("thou shalt have no other Gods before me").
I also agree with the differences in structure and leadership in the Eastern Orthodox church vs. the Catholic church, for what it's worth. As you correctly note, orthodox places much more leadership at the local level; whereas everything from theological meaning to finances goes through the Vatican with the Catholic Church.
I don't belong to Eastern Orthodox church, but I approve of much of its theology. And I like the liturgical aspects of its practice. At least what I've seen in Ukrainian/Russian orthodox settings.