The Halo Wars trailer has been released on the public. It's pre-rendered, obviously, though the official site (also live!) claims it uses lots of in-game models. The game takes place before
Halo 1, following the crew of the UNSC "Spirit of Fire" from initiaql skirmishes to an all out war against the covenant. I'll be interested in seeing how they handle Spartans — I believe within the Halo universe, there's only 16 who survived the bone-grafting process, so there's actually not a hell of a lot of them you can play around with and stay within the fiction of the universe. Obviously, though, they'll be a type of hero unit.
Kotaku