It's funny how singing and voice always get mixed up in these threads.
Jon's never been the world's premier rock vocalist, that spot probably belongs to Freddie Mercury forever.
He has been an ok to good singer in the 80s, but with an excellent voice (if not 200 shows into a tour). Today, he is a much better singer technically, but with a mediocre voice.
What I'm missing is the power, high notes and screaming - a Bon Jovi trademark until the mid 90s. It was part of the awesomeness, but apart from the voice not due to singing abilities.