I realize this covers a very large period so it may be difficult to narrow it down, but I've always been curious about it. The Sumerians wrote about their love of beer, and wine plays a central role in the literature of Greece, Rome and the Bible. Were these beverages anything like our modern versions in taste? What about composition and how it was served?
Hops weren't used until the middle ages. As you say, the flavour of beer would be quite varied depending on the time period you're talking about, but lack of hops is the biggest difference between modern beer and ancient beer. (My source is the Oxford Guide to Beer)
Fun fact: if you'd like to taste something similar to Sumerian beer and know how to homebrew, you can make your own Sumerian beer. It's apparently very sweet and very sour.
Patrick McGovern at the University of Pennsylvania has written a number of articles on early fermented beverages, analyzing the chemicals found in ancient vessels to try to determine the ingredients and process used. He has also consulted with a contemporary brewery, Dogfish Head, to actually try to create reproductions of these ancient beverages.
Among others, see:
A funerary feast fit for King Midas (Nature, 402)
Fermented beverages of pre- and proto-historic China (PNAS, 101[51])
9,000-Year-Old Beer Re-Created From Chinese Recipe (National Geographic)
As a follow-up, did any cultures chill these things as we do today?
Follow-up, I have heard that the ancient Egyptions developed a sophisticated fermentation method to produce beer stronger than 3-5% - and that this knowledge was lost for thousands of years after the decline of their civilisation.
Is there any truth to this?