Well I used to be really good at the fifa games but I seriously suck at Fifa 12. On fifa 10 I had a 75% ratio online, on 12 I don't dare go online as I can on barely beat the computer on the middle difficulty. So in comparison to what I used to be like, yeah I now suck.
Also the CoD games, for a series that is often described as easy or pick and play I just die over and over till the very concept of dying is routine. I'm just bad at them. Yet on Halo, which is regarded as a shooter with a higher difficulty, I normally hit par (as in 1 kill for 1 death), which why not great is at least a step up from my performance in the CoD series.