The seventy-second classical recording: #120 Christoph Willibald Gluck - Orfeo ed Euridice
As always, when dealing with operas in a foreign language, it helps to know the story. Here, the myth of Orpheus and Eurydice is well known and the acts distinguish themselves quite well, the descent into Hades changing from the higher arias of the first act into something darker and deeper, away from the pure sopranos. The other settings have similar changes in music, which work well to create a setting rather than a theme.
The opera having almost only parts for sopranos or high tenors, with other voices limited to the choirs, appears to have been the Italian fashion o the time. Itl imits the character building a bit, but it starts working soon enough once you begin to learn the characters. Musically it doesn't matter much, and makes the piece flow well.
The other side are the ballets that were included in the version I listened to. They don't add much musically - in part because it seems they were added in later - but they work as a nice bridge between pieces.
All in all, this doesn't quite have the high flying moments of other pieces, but as a full performance it flows well, keeping consistent while setting up some good location building in its music.