I could care less about the splitting of the storyline based on geography and POV characters. I don't understand why there are so many complaints about it. It's a moot point at this juncture. Will you complain when GRRM is done with ASOF&I and writes about something other than Westeros?
I also don't understand the "I hate Catelyn" and "Please don't hate Catelyn" threads. These seem to me to be nothing but expressions of personal preference, and, as such, cannot be resolved when differences of opinion emerge. One of the many things I appreciate about of GRRM's writing is that he provides a heavy dollop of reality in character creation, such that each character has both desirable and undesirable qualities.
No, what I thought was weak about AFFC was the level of detail of characters, events, and locations. Sure some chapters sang (viz., The Captain of the Guard and The Soiled Knight"), but for most of AFFC, the writing was substandard when compared to AGOT, ACOK, or ASOS, and the best way I can describe it is "thin".
I also believe that one instance does not make a trend. So, I don't believe ASOI&F is "going downhill" just yet. I will be eager to read ADWD, and see if GRRM is able to capture the redolent and fertile writing that drew me to his work to begin with.