He's wonderful. He has such an effortless voice. I am a singer, and I frequently find myself wanting to emulate him, only to drastically come up short. I always listen to him sing and think "hey, I could sing that song!" only to try, and think "Jesus, that was a lot harder than I thought it would be." He has excellent technique, and I think what makes him stand-out is that he's a tenor, but has the rich timbre of a baritone.
I feel very fortunate to have seen him in Hamilton during previews at the Public. I suppose now that he's doing the role again, it's not as much of a significant claim, but I'll always associate him with that role more than Jonathan Groff.