GamersGate is pretty easy to understand.
There are a group of people who feel that lately a lot of other people have been saying that the things that they enjoy are wrong and bad and that they are wrong and bad for enjoying them and that no more of these things they enjoy should ever be made. Instead of responding to this in a mature, reasonable fashion, they have resorted to aggressively defending their interests by threatening and harassing those they feel are trying to take what they like away.
Now, from what I understand their opposition is generally trying to expand gaming to be more representative of those who partake of it, not change or remove parts of it (though there are certainly people who do want to, they are likely not in the majority and they do not restrict their aggression to such people anyway). Because generally such people identify as feminists and generally many feminists are females, proponents of GamersGate seem to just be lumping all females into the category "enemy", thereby creating a hostile environment in the hopes that no one will be left to take away their toys.
Oh, and there are probably a bunch of general misogynists who are taking advantage of this as well.
Did I miss anything?