It's less because, having listened to Gesualdo quite a lot over a period of years, the unexpected shifts in tonality and sudden dissonant harmonies feel familiar to me. I had time to look over the music before we started rehearsal. And it's coming together faster than I would have expected, on a pure note-level.
It's more because the hard part is going to be making this into music. We had some hints of that last night; remembering that we're singing texts, and that in this, the text is a really, really important part of the music. It takes a little time and a little familiarity to be able to surface from one's own line and hear how it works with the other lines, and how the whole piece works, how it grows and fades and moves to make art and not just the iteration of notes.
I now understand why this piece isn't often performed.