I did it. It probably took me over 20 hours to do it, though, since Legendary is such a hard difficulty. I played around with going back and playing the game over again on Heroic, but I decided against it. There's no telling how long that would have taken!
I've gotten the achievement too, although I don't know how long it took me. I know it was a headache at times!! Does anyone know if there is a stat that keeps up with how many times you died in the campaign? I bet a died like, a hundred times trying to beat the game! =/
I plan on doing it soon, there have just been so many great games that have come out in such a short time that I've been constantly been alternating between them. I always end up trying a game at the hardest difficulty and have beaten the rest of the Halo games on legendary so I'm sure I'll do it eventually.
I haven't done it yet. The first time I played through the game, I played through it on Heroic. I thought about going back through it on Legendary, but I was kind of burnt out on it at the time, so I switched over to Black Ops II for a while. When I get tired of Black Ops II, I'll probably try to run through Halo 4 on Legendary. I want the achievement eventually.
I haven't gotten this achievement, and I doubt I will anytime soon, because I am playing through the game on Normal right now. This is actually my first Halo game, and it's very different from Call of Duty, so I decided to play it through on one of the easier levels first, just to get used to the game play.