There was a lot of neat stuff we will probably never hear anything about. There was apparently a Q&A, and one of the fans asked Sonic Team what their next project is. Too bad we'll never know the answer. They also apparently talked about 25th anniversary a bit and shared the logo.
There was a few announcements. The biggest ones in my opinion though are the SEGA Symphonic Concert announcement for July 2016, Sonic Adventure Music Experience Concert for April 2nd.
and then the event ended with Jun Senoue playing open your heart
SEGAnerds has a pretty good article summarizing the event with a load of pictures
http://www.seganerds.com/2015/12/27/sonic-fan-event-2015/