Just because, my Sinatra story:
1984, I think, early Atlantic City, probably Resorts. Never went back there; it was a company freebie, an overnight with a couple dozen coming down from Long Island.
I remember no details, simply that his voice had obvious limitations, and the songs were mostly overblown crap of a type I can't stand. Every time he got to a note and it seemed like he'd painted himself into a corner and had no chance, he resolved it with something unexpected and satisfying. Every song was the best performance of it that I'd ever heard. It was like the words really meant something.
I don't know how he did it, but that was my experience. Every. Single. Song.
As to Van Morrison, it's been a while and my experiences have been good, but I've always feared and joked that he might stop mid-song and walk off at any moment.
I've also enjoyed the sport of listening hard to pick up clues and figure out what song Dylan is performing before whoever else I'm with does.