In Ancient Greek the Y was pronounced like the German
Ü (U umlaut) or the French U like in "sur"; this is at least what they teach in Germany (maybe the Germans just love their umlaut). It's just the OY (omikron-ypsilon) that was pronounced like OO.
In modern Greek I understand there are lots of EE-sounds around, all the Es (epsilon) and Äs (Eta), the Is (iota) anyway and also the Ys (ypsilon) are pronounced that way. I got the impression that due to all those EE-sounds modern Greek sounds like everybody was smiling all the time, but maybe the Greeks are just such friendly people.Andy