Took me a while but I've finally been able to enjoy the game.
Kept crashing at either first start up, loading screen, or in the initial intro. Actually turned out of be my overclock. Put everything back to stock on my card (GB 7950 WF3) and it run sweet as a nut. Weird because I played Crysis 2 for an hour last night and it was stable as a stable thing, sitting under 50deg the whole time. Even on stock though it still breezes Ultra at 1080p (no AA). Haven't checked frames yet but at a guess I'd say 50-60fps, if not more.
Next issue I had was the pocksee Ubi servers being down, which meant everytime you went into the menu it would fail to connect, then when you try and go back to the game it's like all the rendered surroundings all disappear and you're just left with what I assume is a distant background image. Just figured out though (as said above) that playing in offline mode fixes this problem.
Only done the radio tower and first camp so far, but game looks gorgeous and I do think I'm going to enjoy it when these few issues are ironed out. Lets hope the devs are slaving away now to get it fixed.