Finally got round to watching it!
I have mixed feelings. I LOVE the new HUD and hope it doesn't change much in the final version. The video overlay thing is awesome and exactly what I'd imagine Spartans to be using. The audio sounds awesome too, a lot punchier that previous iterations and it sounds as if the weapons have a bit more oomph to them. Also, was that Steve Downes as Spartan-117? I'd thought he hadn't signed on, but it sounds like he has. If it's not, whoever it is does an excellent job. Musically, they're going to have a MASSIVE task living up to Marty O'Donnell and it's unclear from the trailer if they can. It also looks gorgeous.
I think I like what they're doing with Cortana too, her deterioration into rampancy is one of the key points of the story by all accounts. Her little ballistic bit at the end of the trailer took me aback.
On to the bad, I knew the Covenant were back, I'm slightly disappointed to see Elites working with them again. I'll probably need to read Grasslands to find out what the deal is there, I've just been waiting for the Kindle release.
Also, not sure if I'm keen on the new enemies (the sword/light rifle guy), it would have been ok if it wasn't for the skull thing when his face opened. Although I think I know what the deal is there. Primordium explains that.
More positive than negative though and I'll still be getting the limited edition!
PS - The Didact also sounds exactly as I imagined he would.