Gamestop, IGN, Gamespot, trailers that include in-game gameplay, etc... I compare them all for more accurate data.
Sometimes I'll follow people researching at E3s, Comicons, PAX, etc... usually from these I can actually watch people play the game and I can make observations. Sometimes if I'm lucky and their are early passes to demos, I can get hands on thanks to some people that I know.... (I'm gonna see if I can get a hands on early demo of Resident Evil 6 for you.)