At the Microsoft conference, they announced backwards compatibility. If you purchase Siege this year, you will receive Rainbow Six Vegas 1 and 2 for free.
Ubisoft finally revealed some singleplayer info with the actress Angela Basset in the role as Six, the leader of team Rainbow.
They also did a live gameplay session of 5 developers playing Terror hunt on a new map.
We will have more exclusive content over the next days and interviews with the developers of Siege. Be sure to check back for more reports from e3 and follow us on twitter.