I've got mixed feelings about it to be honest. A graphic update can't hurt and added online co-op will be nice too, but it's being handled by some studio I've never heard of who might try to fix things that weren't broken in the first place.
http://www.joystiq.com/2011/02/04/halo-combat-evolved-hd/
http://www.joystiq.com/2011/02/04/halo-combat-evolved-hd/