ok i bought it earlier today and had the same issue. it just kept saying "cant download" over and over. i tried it from the dashboard deal, from the games on demand section, and from xbox.com. i even waited a while before i tried it again. still nothing.
so i eventually caved after a discussion with @xboxsupport on twitter and called xbox support.
they ran through a few different steps. i tried clearing my cache, redownloading my profile and all that nonsense. nothing worked, so the guy transferred me to a higher up.
she told me that she's gotten numerous calls about problems downloading THIS GAME specifically. she said she's going to promote the problem and have the "tier 3" people look over it. she gave me some phone number and said that they would call me back about it in a few days. being that its so close to the new year, i doubt it's going to be within the 3 day window, but still.
anyways, my advice to all of you would be to call xbox support if you've got an hour to spare because thats how long it took for them to figure out nothing for me, but i assume the larger call volume would grab their attention.
so yea, thats my experience with this nonsense.
i think at this point, i dont even really want the game anymore. i just want my money back.