Allenthar wrote a nice post in our forum about his experience at the Xbox Odyssey event in San Fransisco on the 4th of this month. It focuses mostly on playing impressions and combat events rather than story spoilers, but he does warn that reading it might take away from the first experience of playing the game, so beware.

Unlike some others who have played, he didn't mind the splitscreen modes:

Simply put, Halo looks great and any worries you may have had should be completely dispelled. On another note, I was afraid that Halo would look poor because of the low resolution of the ordinary television. I played for about half of the time on a 18 or so television and even with four players you could still see everything you needed to fight effectively.

There's a very interesting anecdote about some camping techniques near the end of the post; it's worth a read just for that alone.