GamerGate is what happens when women try to shield themselves from criticism by shouting 'sexism'. Anita Sarkeesian is a hypocrite who has little to do with GamerGate, she was before then, and her videos sparked a different row, she is just throwing her weight around now because she can't go 5 minutes without publicity.
GamerGate is basically a call by the community for the reformation of video game journalism. The issue started when an ex-boyfriend of Zoe Quinn, a game publisher, released a detailed blog post about how she cheated on him with five different guys, all involved in the video game journalism industry. A few of these guys are unnamed, and the ones who were named then admitted to having a relationship with Quinn. These guys all gave her favourable reviews and publicity, and pushed her game (named Depression Quest, and a title she used as a method of exploiting Robin Williams death) onto Steam Greenlight, with the aim of getting it onto Steam and making her money. This game is dreadful, so obviously questions were raised, and Quinn covered herself by crying misogyny, getting her friends in the media to publish many articles defending her, and stating that gamers were sexist (which then sparked a response known as WeAreNotYourShield). Quinn also did things like causing a charity project for female game designers to be crashed due to them not funding her project, and apparently faked hatemail, death-threats and doxxing herself (and Phil Fish) to protect her own skin. That is Gamergate, and the media (who are naturally covering up any evidence of corruption) are twisting it into a male vs female debate.