The big news in the latest weekly update by Frankie is that, barring any serious bugs, Bungie is essentially finished with Halo 2. They've sent the game out to be certified ready for production.
While short, this update is full of quite a bit of interesting information about clans, about XBL, and even a tidbit about single player:
As for single player, I am getting my ass handed to me by Legendary. I got to a spot, about ten minutes into the game normally, and have spent three hours trying to beat it. I am not kidding. I foolishly wasted some weapons early on, and now am paying the price. I may start again, take a deep breath and hit it more strategically.
That would seem to backup MSN's comment about legendary being "adamantium hard".