With regard to ecumenism and the eventual hope of the restoration of unity in faith and communion between all the baptized, I'll just say this, from the Roman Catholic perspective, Orthodox are immeasurably closer to us than the most conservative of Protestant Evangelicals could ever hope to be just by the fact of being Orthodox; because like us, you also cherish Marian devotion, veneration of Saints and Angels and their holy icons, liturgical worship and the highest reverence for the Eucharist, prayers for the departed, reverence for the Fathers, the decrees of the Councils etc etc in addition to the basic beliefs in the Trinity, Incarnation, Passion and Resurrection etc almost all Christians have in common. Where we would disagree with you is mostly in the areas of Purgatory (although even most Orthodox admit some form of intermediate purification, even if not by "fire"), the Immaculate Conception (though you call Mother Mary the All-Holy and Stainless Virgin Mother of God) and the Filioque, (though some Greek Orthodox admit the formula of St. Patriarch Tarasius of Constantinople in Nicaea II that the Church "believe(s) in the Holy Ghost, the Lord and Giver of Life, Who Proceeds from the Father through the Son" to refer also to so-called "hypostatic procession") etc and likewise, Divine Simplicity and Uncreated Grace are some points where agreement has not yet been reached between the shepherds of the Roman Catholic Church and the hierarchs of the Orthodox Church.
This being the case, in some ways, the differences with Protestantism seem more simple to understand to the average Catholic in the pew; after all, if Protestants reject Purgatory, they also mostly reject all prayers for the departed, consistently although incorrectly. If they don't believe Mother Mary has always been Immaculate, they also fancifully claim it's because She is not All-Holy and Stainless, but supposedly was a sinner. Also, in some cases, and despite the dialogue that has gone on at the highest levels for a while now, it's genuinely not clear to us looking in from the outside whether Orthodoxy as a whole holds these matters (Purgatory etc) to be acceptable theologoumenon or entirely erroneous doctrines. Bp. Kallistos Ware, whom I respect immensely, seems to suggest the Immaculate Conception could be regarded as a permissible belief for an Orthodox to hold. His Eminence, as is well known, has written "all Orthodox are agreed in believing that Our Lady was free from actual sin ... The Orthodox Church has never in fact made any formal and definitive pronouncement on the matter. In the past individual Orthodox have made statements which, if not definitely affirming the doctrine of the Immaculate Conception, at any rate approach close to it ... the great majority of Orthodox have rejected the doctrine, for several reasons. They feel it to be unnecessary; they feel ... it implies a false understanding of original sin ... From the Orthodox point of view, however, the whole question belongs to the realm of theological opinion; and if an individual Orthodox today felt impelled to believe in the Immaculate Conception, he could not be termed a heretic for so doing. But Orthodoxy, while for the most part denying the doctrine of the Immaculate Conception of Mary, firmly believes in her Bodily Assumption." This is one of the few things many Catholics who first begin to inquire into Orthodox theology immediately notice and theological discussion at the highest level would certainly help clear that up.
