A big difference I think we have right now is goal threats. With Giroud, Walcott, Campbell and Ramsay (as long as a midfielder and not a winger) on the pitch at once means we have four goal threats. Previously, Cazorla and Ramsay on the wing were simply not consistent goal threats and it was easier to stifle us as we relied on pretty much Sanchez and the striker.
We have got really good defensive shape and we're shutting City down all over, apart from De Bryne, who I think needs doubling up on for the last 25 mins.
We're creating so many chances, but we really need to kill the game off. I have to say that I've been very impressed with our performance thus far, given that we're missing Cazorla, Coquelin and Sanchez. City have not looked up for it at all.
I also think that nobody is getting isolated, Ozil is dropping deep to join Flamini and Ramsey when we lose the ball, Walcott and Campbell are working hard on the flanks and dropping back to ensure there is no space and no FB/DM can get isolated. And it means we aren't getting ripped apart by teams, but have the confidence to soak up pressure and hit them clinically on the break. With the pace and goal threat you mentioned it is definitely all coming up Milhouse!