I missed this one in August, but just stumbled across this Bungie podcast interviewing Peruvian A.I. wiz Damian Isla about Halo 2&3 A.I. It's a good listen.
http://www.bungie.net/News/content.aspx?type=topnews&cid=12705
The Halo series gets a lot of attention for it's multiplayer, but this podcast highlights the huge challenges faced in developing the single player campaign -- lots of characters on-screen at once strategically using a variety of equipment and vehicles, and even running around on moving platforms. No small feat.