Agreed. His material wasn't always the best, but he had a fantastic voice. Very resonant, sounding like a baritone in the low register, and a tenor in the high register.
I may have told this story here before: I saw Jack live circa 2007. He did a version of "Our Love is Here to Stay." The first chorus was very quiet and restrained. He was walking through the audience and singing to people along the way.
Just when the second chorus kicked in, with the drummer going to the ride cymbal and the bass walking, Jack gets right in the face of an older woman, skips the first line (It's very clear), and let's out a high Robert Plant wail from out of nowhere. I thought she was going to have a heart attack!