My friend Jake, a guy who wouldn't stand a chance against the average halo player in my area, or at least when he first started playing, played Halo on Legendary for his first play through. He did it with relative ease by just running around shooting the out of everything.
Either not on Legendary, or he's a lot better than he makes out. Halo 1's Legendary wasn't too bad, to be fair. So go play Halo 2 on Mythic.