I think the thing I look forward to most about this game is knowing that Yahtzee will most likely write an extremely hilarious review of it.
I've always enjoyed the other games, but for some reason I've always hated Halo's multiplayer. There's just something about it that annoys the piss out of me, and I've gotten more and more frustrated as they focus more and more on it and leave us shooter fans with no friends out in the cold (alone, as always). In contrast, I've usually found Halo's cooperative was very fun to play with a friend in split-screen (online it's less fun) because you can get drunk and put it on Legendary and see how ridiculous you can be.
In short, Halo will always be THAT game to me. That one that I'll always enjoy playing with friends (in the SAME ROOM), but if I tried to play it alone I would get bored and put in something better.
So this game announcement, while completely unsurprising (I'm surprised that people are surprised), doesn't really bother me in any way, but I'm not exactly excited. My curiosity has been piqued. Maybe they'll do something new (ha).