This E3 Trailer shows off the gate opening animation what everybody who has been following this game has wanted to see. And I think it looks as good as could be expected. I am not sure when the game is set, but I suspect that it is set after the final episode of SG1, because I know the developers have licence to practically do what they want with the franchise.
Still it is looking good and I only hope they do something dynamic with the level design and AI. Otherwise I can see this playing through like every other recent FPS (linear levels with stupid AI opponents).