My take on James is that in the right set up, he has more potential than Mata and I'd prefer him to Ozil. I think people have been very very harsh on him since he moved to Madrid. It isn't easy to play for that club even at the best of times, and even if you're playing in your favoured position which he hasn't.
He's a majestic number 10, not one of those who goes missing in big games and struggles to impact game.. he is physically more robust than Ozil/Mata and he can be very direct when he wants to be. Problem for him has been trying to play for a side which has such a fixed attachment to the 4-3-3 and he was a poor tactical fit for Madrid. He's wasted away a lot of valuable years.
His issue is that it is hard to see which modern day elite side is crying out for a number 10. We are going 4-3-3, and even if we did go 4-2-3-1, we could get Griezmann.. who is superior and more versatile to James, he can't go to City. Chelsea have been linked to him, but where would he fit in a 3-4-3? if Chelsea went 4-2-3-1 it would be pretty awesome.. but why tweak a winning formation? If Arsenal lose Ozil, he'd be a brilliant replacement but I don't see them being able to afford James, Liverpool like wise.
Europe wise, Bayern could probably afford him but where does he fit in.. they're a 4-3-3 side as well. They could shift to 4-2-3-1, but Thiago-Vidal.. is it defensively strong enough.
Feel for him, he's a potentially great player - but am struggling to see where he would fit.
If United got him..
We would have to sell Mata/Rooney which is totally fine by me, but he'd have to play second fiddle to Mkhi out wide, when we play 4-3-3 and would only start against teams we go all out attack against.