I picked it up at midnight yesterday and I've been going through the campaign and I'm blown away by it visually.
Everything looks great and the detail is awesome (like the ID barcode on the marine chest plate)
My only complaint is that the allied AI will get stuck or stay behind at points where they didn't in the original, and then they'll come up to "help" after you've killed everything.
This has happened more than once, but it was most note able as MC on Delta Halo right after you have to get out of the scorpion, all the ODST's and regular marines don't even enter the temple. It was also noticeable on Quarantine Zone as the Arbiter. None of the allied Elites follow you anymore.