So the first thing to change would be the gods - dumping the stock D&D gods and replacing them with the classic Greek deities.
Equipment could be handled differently with the whole bronze/iron thing but I don't think that will really be necessary as bronze could be treated as normal equipment while iron could be superior or masterwork equipment. Plus I don't want to have to worry about fiddly things like breaking on a 1 and such.
Races - well Fantasy Greece still needs to be mostly human. Elves & Eladrin can live in the woods, gnomes in the hills, dwarves in the mountains, halflings in some valleys. Half-Orcs could be from anywhere (I can see an Orcish empire in the area of Turkey or thereabouts). Dragonborn might be from an island nation out in the Atlantic (Atlantis was run by lizards!). Goliaths and Shifters and Devas could also be from just about anywhere. Minotaurs would be from Crete of course.
Classes - anything goes here, I see no need to rule out anything. The psionic power source might be limited to Egyptian characters, I think that would be interesting to have it foreign and exotic to the mainland campaign area. Primal powers would be limited to non-urban characters but that's not a huge obstacle as pastoral Greece has a lot going on. Thracians might be a good source for this too as I see them coming across as barbarians in a lot of ways.
Environment - The main campaign area would be a fantasy version of Greece with several city states separated by dangerous wilderness and the ruthless competition between them. Gods favor different cities over others, various monsters ravage the countryside, and armies occasionally march forth to enforce one cities will over another. I see this as a post-golden age Greece where legendary kingdoms and heroes have all fallen leading to a new dark age, which fits well with 4th editions points of light setting.
Adventures - These could cover some basic routine dungeoneering to begin with then spread out across the Mediterranean. Northern Eurpoe would be the home of Drow and Giants, Africa could have dinosaurs, and gates to other planes could be found in out of the way places. The Norse gods could come into play at some point, and so could the Egyptian pantheon although I might make them a little different.
This would be a flavored, not totally by the book campaign but it would definitely take a different tone than regular D&D, at least that's how I would plan on running it. Lots of little differences than a standard medieval game.