I agree that she shouldn't be equated to Rush (nor should Olbermann be equated to Rush), by any stretch of the imagination. But that's mostly because Rush doesn't call himself a journalist and makes no bones about the fact that he's wholly one-sided.
Still, Olbermann engages in name-calling and insult hurling. He is--imo--right at the top in that category. He shouts down guests that disagree with him, just as O'Reilly does. And he's got an agenda, as does Maddow, as does Hannity.
I would agree that you can compare Olbermann to O'Reilly. I find O'Reilly a much more unpleasant person personally, but that is a subjective judgment. Rush is a different animal, and Beck is. . .well, different.
And yes, Maddow is an unapologetic leftist. But I've found her to be someone who tries hard to be fair, and I appreciate the fact that she's a smart woman, unlike say Hannity, who is an idiot.
I've seen many interviews on her show with people she violently disagrees with, and she lets them have their say, does not interrupt (although being prepared, often challenges them) and is unfailingly polite -- even with someone who tells her that being gay is a sickness, perhaps unaware that she herself is gay.