The best I have ever seen them play was when they put 5 or 6 past Madrid in what I think might have been Jose's first "classico" and then in a Champions League home tie against Arsenal - where Arsenal just couldn't get the Ball off them and Arsene's team ended up in the same state as the La Liga mid -table cannon fodder. I don't think they have hit those heights for a while now though.
I think that if when they are knocking the Ball around our final third and we can steal it and spring forward we can cause them plenty of problems. Also, they are not the greatest at defending set pieces. I think their keeper is average at best and might drop a bollock; and I am pretty sure that Kun, Negredo and for this game especially, Dzeko could rip Mascherano a new one.
We also have built up a bit of a fear factor. All the headlines in the Catalan papers the day after the Draw was made headlined with " Oh no, it's City".