Props for manning up. I think opinions of his coverage abilities will differ depending on what you consider "very good" in coverage for a SS. Certainly he could be better. Do you ever wonder why so many people believe he is just inept in coverage? I do. I'm convinced it's because people see him in frame when the other team scores - and he can be attributed a good number of TDs allowed. Of course, how important do you think that is? Say Brees kills us down the field with dumps to his FB, and then in the red zone hits his TE over a hapless Bradie James, and Roy misses the tackle for a TD. Clearly Roy could have prevented the TD, but if assignments had been followed on the TEs, the drive could have been stopped much earlier.
Giving up TDs is really being a victim of circumstance. Just as scoring them is a benefit of circumstance, considering one player could do all the work down the field, get it to the 1, and a RB punches it in. (ie Emmitt and Michael) Once you get past the TD thing, and evaluate him comparatively, he comes out very well. Plus, he's flat out a playmaker.
Something else that contributes to the negative image of not only Roy Williams but also Sean Taylor is the passive cover two system that both teams played. Often because of the incompetence beside them, they are forced to cover about 3/4 of the field. Due to the coaching staff's inability to change, and insistence on playing that passive zone instead of compensating for deficiencies in coverage by applying more pressure, these guys are continually forced to cover for extended periods. Whereas a guy like Reed is able to play center field and let his dominant front seven work magic in a pressure defense. No safety can do what Roy and Taylor were asked to do last year.