Just returned from Gamescom, there were Sonic 4 (XBLA), Sonic Free Riders, Sonic Colors and Virtua Tennis 4 playable, even if SEGA wasn't at the show.
Unfortunately I didn't play Sonic Free Riders, there were too many people waiting in the Kinect queue. But I saw a lot of it, it was the same level (and maybe build) that we all already know from youtube videos. I made 2-3 videos but I won't post them at the moment, there is nothing new you could see I think. People had quite difficulties to play it (in general for Kinect games too). Can't say more about it without playing.
Virtua Tennis 4 was there in playable 2 player mode or with 3D. I played with the 3D one, which was pretty cool. The game itself, hmmm, maybe a Wii Sports with better graphics. But strange gameplay as you all saw in the video from Segastuff on the mainpage. I had some difficulty to play and would prefer a normal Virtua Tennis instead of this. I made a video, but am unable to upload it at the moment. But you can't really saw anything new that you saw from the video from SegaStuff.
Sonic Colors (Wii), very very nice. Got to see the power of a wisp (yellow) and a some new stages that I haven't seen before (but don't know if they were new). Very good game.
Sonic 4 (XBLA), there were playable the first 3 acts and the boss. I think it's the same build as E3, Comic Con and Summer of Sonic. But it was the first time I saw it live and I really looked forward to it. It's great to play and I love the homing attack in the game. Only a few Sonic movements are a bit strange, but you all know them from various youtube videos I suppose. I made some videos too, but again, I think there is nothing new to see. Overall I enjoyed it really much.
If you want I can upload some pictures in the weekend and maybe some videos.