Definitely an exciting announcement. The most notable thing about it to me is that it is another first person shooter, not a third person or squad based shooter like the rumors have been saying. We'll keep our eye on the game as it develops towards its launch in Fall of 2009.

Article:
http://www.gamespot.com/xbox360/action/halo3untitledodstgame/news.html?sid=6199075&om_act=convert&om_clk=newsfeatures&tag=newsfeatures;title;1