The FBI has released a heavily redacted 173-page PDF of GamerGate documents under FOIA. Much of the material has any identifying information stripped out, but it's clear that many of them are explicit threats and other harassment.
Many of the items include rants about feminists, and a few threaten school shootings and other threats that were taken seriously. They also look at a number of Twitter accounts that were doxxing people involved in the controversy, and they take case reports on accounts Twitter shut down in response to harassment and threats. In some cases, it appears that Twitter supplied information about the accounts to the FBI.