Eh, I like Marissa, and I've worked on projects (the 2010 websearch visual redesign, and doodles) for which she was the executive sponsor. No, she's not a nice person, and most likely she does not give a shit about you as a person. But she is very often right about her design opinions, and when she's not, she'll listen to data.
I don't think Yahoo particularly needs a nice person as CEO right now. Their culture is dysfunctional enough that they probably need a Steve Jobs type, someone with clear opinions who's willing to ruffle a lot of feathers (and make a bunch of people quit). Steve Jobs wasn't really a nice person either.