The first proper gameplay footage from AvP3 has been released via Gametrailers in the way of a demo walkthrough by a member of Sega:
The footage is of the Predator mission. It shows off the vision modes, the trophy kills, the leaping system. Also shows us the PredAlien (which unfortunately has some deleted tendencies of Chet). There are two clips of footage and you can find both streaming and HD download links in our forum. Thanks to Chet for the news.