I feel like most medieval discussion I hear is focused on Western Europe, along with some talk of the middle east and occasionally mentioning the area where modern-day Russia (rus?) is. But I would love to know what was happening closer to the Mediterranean during that time period. Christianity was spreading, but was it feudal like Europe? Was it fairly similar to how the slavic region was developing? (I know the languages are intertwined to some degree). Finally, did any great art or thinkers come out of this location at this time, and why don't we here more about it?
Christianity was spreading, but was it feudal like Europe?
In the eastern Mediterranean and Middle East, Christianity (or at least Christendom) was in retreat after about AD 629. Christianity was brought to Greece by Paul the Apostle around AD 50. By the 'Dark Ages' or Early Medieval Period, Christianity had already spread to those areas controlled by the Roman Empire, and had been there for some time.
From the second century BC until AD 1204, Greece was under the control of the Roman Empire, who's capital was moved to Byzantium in AD 330 (and the city renamed Constantinople). The Roman Empire in the east is often referred to as the Byzantine Empire after the fall of Rome. The center of Greek culture, then, shifted to Constantinople, which is where you'll find much of the great art and thinkers of the period (but not all). From the first fall of Constantinople to the Fourth Crusade in 1204 to the second fall in 1453 to the Ottomans, Greece was partly under Frankish and Venetian control, contested by the resurgent Byzantines. By the early 1400's, the Ottomans had begun pushing into northern Greece, and by 1540 had captured the last of the Venetian strongholds.
You might want to look into the FAQ's entry for the Byzantium Empire.
Just to be clear, are you asking about Greece during the 'European Dark Ages' or the 'Greek Dark Ages'?