Sadly, I think the coop issues are a split screen thing, there's been talk of that for a while now. Just another thing to iron out.
And I take it some people here must have played the Guardians beta by now. I played a few games last night and well... its certainly different. And I guess I have to eat my words on ADS not being a thing for all weapons.
The stupidly fast pace of it all combined with the new features means it doesn't feel all that much like Halo. But Halo 4 didn't either IMO. And in contrast, I'm actually quite enjoying Guardians, so maybe that's not such a bad thing.
There's a real sense of team play as well thanks to the new mechanics that I really like. Clambering, thruster packs, and the hovering thing when you ADS mid air all make for great synchronisation in the team. Storming enemy positions with each member doing something unique with those abilities is a whole lot of fun. That and there's just clever stuff with a lot of the mechanics, like not being able to recharge your shields while you sprint for example. Little things that keep it from getting too hectic.
I think I'll quite like it, all in all. If I want to play my slow paced, traditional Halo I've got the MCC with all the content I'd ever need only a disk change away. I'm interested to see where they go with it.