Played through the wee hours of the morning on heroic and got to mission 8. This campaign is a dream, buttery smooth, wonderful art, mystery, best in series movement and the AI if you take charge like you should is wonderful and a real couple of steps up IMO.
Now I have to go to work and try to put the story out of my mind. As an EU follower this is the best campaign in the history of Halo. The critics are wrong, the Halo 4 meme of 9.8/10 applies here without the meme. Do yourself a favour and play heroic. Everything from the audio being sublime for the soundtrack to insanely quick load times this game is clearly a studio hitting its stride and putting a confident foot forward.
I couldn't be happier.