Are Orthodox Christians all the same faith?

The first answer was awsome. Very clear and informative. One exception is that Rome & some of the OE Churches have returned to limited communion. Catholics are allowed under special circumstances to also commune at EO Churches and they at ours. Never really happens as the EO won't allow. However the Catholic Churches who are offshoots of the OE Churches are often much closer to their couterparts abd you do see joint Liturgies. I also know many OE here in America commune at EO Churches whick I think is not allowed.

Orthodox are all the same. I am Antiochian Orthodox but we have Russians, Greeks, Romanians, and Serbs that also come to our church. The Eastern Orthodox and Oriental Orthodox are not in communion but their beliefs and liturgy are nearly the same. Nowadays, most Eastern and Oriental Orthodox believe there was a misunderstanding in language during the Chalcean Council. Both Oriental and Eastern Orthodoxy are different from Catholicism and Protestantism in their definitions of sin, hell, and heaven among several other things.

Eastern Orthodox churches all share the same religious dogma. Where they vary is language and with regard to some rituals and customs. For example, some churches are on the old calendar. Young male Macedonians, Romanians, Bulgarians and Greeks dive into water to retrieve a cross to celebrate Epiphany. Russians use gold crowns during weddings, Greeks use more simple ones. They are all religiously the same however.

Actually, the Coptic Church is one of the Oriental Orthodox, there's also the Ethiopians, the Malankar (I think), and others who escape me at this point.

However, it is incorrect to argue that the Orthodox are split into two sects. The so-called "Eastern" Orthodox (which I am), would simply say that the Oriental Orthodox is another break away group, like Rome, but which retains much more of their Orthodox roots.

The churches your speaking about are all the same in faith and are all Eastern Orthodox. The reason they have different names is because of the ethnicity/culture of the Orthodox who attend that Church, but they are all united in one faith.
In my opinion the ethnic denominational churches will slowly change their name to Eastern Orthodox Church because once the immigrant population pass away, the next generations don't know Greek, Russian or Serbian anymore and will want their service in English. As a Greek Orthodox Christian, I think that would be a great idea!

Officially all the Eastern Orthodox Churches share "one Lord, one faith, one baptism," and this is manifested by intercommunion among, say, the sees of Jerusalem, Antioch, Alexandria, Rome (before the Schism, she received the highest honor among the sees at councils), Constantinople, Georgia, Kiev, Moscow, Athens, Washington DC, Paris, London, Tokyo, Bulgaria, and so on. One of the recent blessings the Lord bestowed upon the Orthodox Church was a restoration of intercommunion between the estranged sees of Moscow and the Russian Orthodox Church Abroad, which separated due to the Bolshevik Revolution. We all believe (canonically/officially) the same thing, or rather, we all believe in one Lord Jesus Christ, in more or less the same way.

With regards to the answer of @mxyzplk: in America, due to the immigrant nature of our population, Orthodox parishes unfortunately can become ethnic enclaves rather than Eucharistic communities. This is a heresy condemned by the church: it is called ethnophyletism. This is not to say that ethnic communities dedicated to preserving a real culture in the midst of our consumerist so-called culture are bad; but they must be distinguished from the work of the church. I have never personally encountered this problem in my life in the Orthodox Church, thank God.

There are other churches with the name Orthodox, among them notably the Ethiopian Orthodox Church, the Coptic Orthodox Church, the Syriac Orthodox Church, and the Indian Orthodox Church. The Coptics, Syriacs, and Ethiopians do not accept the council of Chalcedon, so they are not in communion with the Eastern Orthodox. Confusingly, they are collectively called "Oriental" Orthodox, as opposed to the "Eastern" Orthodox. There is nowadays an ongoing dialogue between the Eastern and Oriental Orthodox churches, in hopes that perhaps our separation is due merely to misunderstanding or language issues. (Cf. orthodoxwiki.org)

This kinda falls into general reference territory. There are two major groups of "Orthodox" churches.

The Eastern Orthodox Church is one large group of churches that share a common theology. It separated from the Catholic Church (or vice versa, depending on your POV) in 1054 AD.

Thus many Orthodox Churches adopt a national title (e.g. Albanian Orthodox, Bulgarian Orthodox, Georgian Orthodox, Greek Orthodox, Russian Orthodox, Macedonian Orthodox, Montenegrin Orthodox, Romanian Orthodox, Serbian Orthodox, Ukrainian Orthodox etc.) and this title serves to distinguish which language, which bishops, and which of the typica is followed by that particular congregation. In the Middle East, Orthodox Christians have also been often referred as Roman (or Rum) Orthodox, because of their historical connection with the Eastern Roman (Byzantine) Empire.

They are the "same type" of church in that they share a theology, but they tend to be ethnically tied - if you go into a Greek Orthodox Church in Texas, you'll still need to speak you some Greek. They don't have a pope, but the group of all their bishops are considered to be the ruling body of the church.

The Oriental Orthodox Church split off earlier (451 AD) over the Council of Chalcedon.

Despite the potentially confusing nomenclature (Oriental meaning Eastern), Oriental Orthodox churches are distinct from those that are collectively referred to as the Eastern Orthodox Church. The Oriental Orthodox communion comprises six groups: Coptic Orthodox, Ethiopian Orthodox, Eritrean Orthodox, Syriac Orthodox, Malankara Orthodox Syrian Church (India) and Armenian Apostolic churches.2 These six churches, while being in communion with one another, are hierarchically independent.

This is a pretty small group however; most Orthodox churches you'll see in the West tend to be of the Eastern Orthodox breed.

These churches are all the same faith in the sense that they recognize each other are Christian, but the Eastern and Oriental Orthodox branches are not in communion with each other (or anyone else, I believe) and consider other branches to be schismatic and more-or-less heretical.

There are a lot of churches with similar names and variants. Of course they are mostly synonyms, a trivial canvas of local denomination names and sub-denominations indicates you have to be quite specific. A commenter asked about "the Coptics;" there is a Coptic Catholic Church and a Coptic Orthodox Church, for example.