I don't think he's "bad," but he is definitely hesitant to come up and tackle, which is something that would prevent him from becoming a NEP.
He's defended more passes in the last 2 yrs than about 95%+ of all CBs, with 36 total.
19 in 2013, and another 17 in 2012. Actually, he's defended 19 (2x) in his career, 17 (2x), and 25--once you take the one bad year out in PHI where he only started 2 games. Those are 5/6 pretty good seasons, at least coverage-wise in passes defended.
Either way depending on specific opinion, he's probably not a good fit here due to the hesitant tackling issue. I wouldn't consider numbers like that "bad" though, especially when you factor in his INTs which have given him 3+ in 5/6 seasons, and TDs in 4/6 seasons.