He was so respected twenty years ago. It's really a shocking fall.
Not really. He's always sucked because his top priority was being an attention whore more than anything, so he squeezed every last drop of attention and good-will possible out of the sheer luck of being Mayor during 9/11.
He ruined a classic 'Seinfeld' episode for me!
That episode does not portray him positively at all.
I disagree. It makes him appear as a sympathetic victim of falling for the low-fat yogurt marketing, and even then it's Kramer's fault for that to begin with. And it's all in contrast to Dinkins making a massive political blunder, which was Elaine's fault.
The impression I got from the episode is that it was dunking on Kramer for being a dunce and thus helping get Giuliani elected. It's obviously not pro-Dinkins but my thoughts were that the writers were definitely not voting for Giuliani. Seinfeld is not a show where the characters' actions typically lead to a positive outcome.