Monteverdi - L'Orfeo
In some respects the first opera, this sits on the cusp of the renaissance and the baroque. Even the way it is written and the instruments are notated are unclear to us, so there are still major disagreements about how it was meant be performed - but with drama is always good in opera, and the Italian recording I am listening to has that in spades, and quite eclipses Gardiner's recording as a result. I may upload it for you, in a few days.