I listened to some recordings of Alessandro Moreschi, apparently the last castrato and the only one to have recorded some tunes. Let me say first that I've been curious about the vocal qualities of castrati after hearing descriptions. And let me add I know nothing about singing and cannot comment on his technique. Also, he didn't have operatic training but sang in the choir at the Vatican.
To me his voice sounded like a young boy, but nothing special. A bit creepy to asscociate that voice with a grown man ~50 years old. I've read that in some of these recordings he uses some odd techniques that have been explained as devices to take advantage of the acoustics of the Cistine chapel. A curiosity.
Thinking is overrated