On the one hand, I believe that talking about problematic media representations is important. In this sense, I value Sarkeesian's work and support her cause. On the other hand, I do not necessarily agree with all her strategies and conclusions. Some critics note that she focuses on the most obvious examples of sexism and ignores more complex and/or empowering representations of women. Sarkeesian also does not talk much about media consumers' agency and how they might interpret media representations she bashes. I personally do not think that gender inequalities can be eliminated simply by analyzing media representations, since these representations and reactions to them are so complicated.
All that said, the attacks on Sarkeesian are terrifying and disgusting. No matter how much somebody disagrees with her, they have no right to express their feelings this way.
The violent negative reaction that Sarkeesian's work has provoked, to me means one thing: she is on to something. Sarkeesian talks of how video games reinforce misogyny, and - lo and behold - anonymous gamers respond by graphically describing terrible things they will do once they get to her. Hm, in my world this is called misogyny, indeed. This whole situation shows once again how dominant masculinity in our society is intertwined with violence, and the feeling of entitlement to women's bodies and voices. A woman says something men don't agree with, and they react by trying to shut her up. That's the story of the fight for women's rights in a nutshell. I believe that, simply by virtue of exposing all this hatred, Sarkeesian's work is important.