The only reason he is a "post-hype sleeper" is because the Mets did a terrible job of introducing him to the majors and giving him regular ABs to get him settled in. Indeed, it was their own foolishness that lead to his value plummeting. Had they given him the job over Shawn Green (and were it not for an untimely injury), we might be talking about the potential of him being another brick in the Met's young foundation. Instead the Mets overreacted to his "attitude issues" (which included a rap CD, being so outrageous as to high-five fans, and pissing off Billy Wagner [which, when taking Billy's sense of veteran entitlement into account, it seems that any rookie who failed to bow at the altar of his veteran greatness and hand-clean his locker would provoke such a reaction]).
In sum, the only reason he is a post-hype sleeper is because of poor handling, not poor performance. The blame should be placed entirely on the Mets FO for taking an extremely valuable asset, reducing it's value through mismanagement, and then trading it at the nadir of its value. Poor player management and even worse roster and economic management.