I've seen many of these threads...
Anyway, like a few of you have said, CoD and Halo have completely different aspects to them. Halo is futuristic, has aliens, has different guns, and just has a different sort of plot than CoD. CoD though, in my opinion, is a bit of an average game. Just get a basic gun, (most do the same thing, so which one you pick is almost irrelevant), shoot two shots to the body in the opponent, throw grenade at others, repeat steps one and two. The campaign is pretty much the same as well.
So, those that say it's becoming CoD, really need to open their eyes a bit.