So, there's like three persons on this board who've tried co-op?
Alright then, it's your loss. But please don't come complaining about disadvantages that hardly matter in the scope of co-op-gameplay. You're preaching to the choir. Halo is a popcorn game, it's polished, perfectly marketed and it's story, pace and plot model are pre-chewed to dissuade thinking, since the regular Halo gamer is fiftteen, pasty and thinks Peter Jackson's Lotr is the height of the movie medium. Depth is tacked on later on with comics, args, novels etc, while in the actual games everything is done for the sake of gameplay, like HL 2, the plot is a pretext to constantly offer new obstacle courses for the player - an old mechanic, but taken to the peak by Halo 2. Despite all that(or maybe because that) it's a perfect group activity, a continuation to beer and FILA openings.
Call me a populist, but it's not like the franchise is cutting on games with actual depth, Halo is the only decent console fps. It'd be nice for people to actually appreciate it for what it is, for what it tries. I'd be along with you folks on the hate train if Bungie actually were like Molyneux, but they've said before that it's just a first person shooter, not an epic scifi vision for the new generation.