4. The storyline
The big news is it's a branching storyline complete with multiple endings. So much for those traditional accusations of linearity. Choices won't be a simple case of choosing one option or the other either - you'll be forced into tough situations where action is required and often it'll be your own skill will be the deciding factor. What's better - or worse if you're rubbish at CoD - is that friends and enemies will live or die based on these moments.
5. The weaponry
It's futuristic, but maintains the traditional Call of Duty bombast. No insubstantial laser blasts, but some interesting technology. There's a sniper rifle that packs a backscatter scope that allows you to see through walls and a charged shot that sends several bullets out in quick succession to cut through said lumps of concrete.