Well I'll be damned!
So I've been sitting here all day (on and off) trying to get this to finish downloading, got stuck with 200mb's left. Been reading this thread and twitter and someone said to make more hardrive space. I'm like... that won't work, I've got 150gb left. I remove some other games I haven't been using, because it can't hurt right? Taking my free space up to 180gb. It started working straight away.
Anyway, I should be in the game shortly. Just thought I'd put that out there - it may or may not work