Aside from the fact that PFF is a very controversial site that can produce absolute garbage at times, and that we really don't know whether McCourty only gave up 5 receptions playing safety or not (as much I credit the secondary's turnaround to McCourty rather than Talib, I find that awe inspiring number hard to believe) I think that McCourty is indeed a stud DB.
Judging by nothing more than the eye test alone, I would probably give him the following ratings on a scale of 10, which are obviously open for debate:
2010 season--9
2011 season--5 for the most part, jumping up to 6--6.5 by the end of the year playing FS. I also believe that a lot of his failure that year was due to very, very poor safety play
2012 season--8
I think these ratings are fair, and I think that 2/3 seasons he has played very well. In the 2010 and 2012 seasons he has definitely lived up to a 1st round draft status in my mind. I just think that there was more in play for the 2011 season that some are realizing, but all in all I think he is a very valuable addition to the secondary.