I'm afraid that if you look into the expansion pack, you will find that the Atlanteans, the only civilization added, will be a carbon copy made from older Greek mythologies. But there are numerous additions to all the other civs, including the Egyptians. Nonetheless, you should not be looking for a History lesson when going for a Strategy game. Actual information is secondary, whereas gameplay and fun are crucial.
Try playing Vanilla out a bit more, and if you're still hesitant - don't waste your money!