Nice! Got me beat. :) I remember the first MW having the grenade spmming too though? I still say COD 3 was worse, but that's splitting hairs. They were both pigs. I have never played Halo 4 but Halo 1 legendary was hard for me. The worst part was in a hanger of sorts. Waves of enemies to the point of absurdity.
I don't remember much about CoD 3, I got it with my launch PS3 and when it came to playing it again on the 360 for achievements I just couldn't be motivated.
That said, Halo on Legendary is always punishing. Really challenging in its own unique way thanks to Bungie's gameplay.