He had a cool voice in the cartoon, Scatman Crothers, the man who had previously been the voice of Hong Kong Phooey (a childhood favourite of mine), and the guy who gets killed by Jack Nicholson in The Shining (spoilers). This guy was just too cool for school, and, by extension, so was Jazz. It helped of course, that Jazz was amazingly cool and awesome in the G1 cartoon. Always at Prime's side, like his Tech Spec bio states he is Prime's right hand man (even if the comics eschewed this notion and made Prowl Prime's go-to guy instead). He was always in the thick of the action, was Jazz, fighting alongside the others, yet always standing out looking good. It helped that he was in some very cool episodes too, one of the best being The God Gambit, where he keeps on explaining to the people of Titan that Transformers aren't gods, and that they don't need to be worshipped. He did it with style, though, as he did everything. It's his motto after all.
Sadly Scatman died in 1986, and the cartoon makers, quite rightly, dropped Jazz quietly from the cartoon, although he is visible in the early season 3 episode occasionally. After that though, Jazz disappeared, like I say though, only rightly. If Scatman couldn't voice him, then he just wouldn't have been the same.
Jazz was never going to get much criticism from me, due to good old fashioned nostalgia. Thing is though, there's not that much, if anything to criticise anyway. The toy is a classic of the genre, and in the cartoon at least, his Tech Spec bio has been almost rigidly adhered to. He could have been allowed to do a bit more in the comics, maybe. He was lobotomised by Galvatron, though. I guess that's not the worst excuse in the world, is it?