Our conductor made something clearer to me about the Carissimi pieces we're doing. I found them really easy to sightread, and could tell exactly where to press into the notes and where to back off; it all feels very open-throated and pure, and being in the middle of those 8-part chords is, for me, almost trancelike. Which is not unusual for pieces written during that time period, as that was probably part of the intent. The written music shapes how you sing it. (It also helps that I listen to/sing a lot of early music, so I know how it's "supposed" to sound.)
Once again, there's actual theory backing up the way the music felt - Matt pointed out that there are hardly any dissonances in either piece. They're all very open major chords, so the difficulty is only in the tuning - I think that's the "purity" I felt, and maybe the trancelike state, because I was concentrating on how the thing tuned.
Tuning is one of the things that's easier for me, so I think that affected how I felt about the pieces, too.