Teaser trailer here:
http://www.bungie.net/News/content.aspx?type=topnews&cid=15574
While I’ve never really played any of the Halo games (I played Halo 1 for about ten minutes in a store once), this intrigues me.
It’s not a new game. It’s almost certainly maps/forge-related.
Besides, you should play Halo. The multiplayer experience is the best online experience available and the gameplay is great.