IGN got their paws on a demo of Sonic Adventure 2 and told us their first impressions of the game. You can read the article here. Also, it seems that we may be able to play the demo!! Here's what they said:

.....There will be two things immediately noticeable when you lucky readers have the oppurtunity to play the demo version of Sonic Adventure 2 this month......

I may be reading it wrong, but it sounds like we'll be getting a demo of the game with the January ODCM, on sale December 26th! Keep checking IGNDC for more info.