Harry Kim is one of the most hated Star Trek characters.
Not so much Mary Sueishness. But that he's a really dull character, and I think was actually miscast. Whenever an episode focused on him it was usually a lot of very generic soap opera style acting between the characters.
He's not as hated as Neelix but is easily one of the worst parts of Voyager for me.
It is fun to watch all the bad things happen to him. He kind of reminds me of Wesley Crusher sans everything working out his way.