To me the most disconcerting thing about what the Chinese are doing is their targeting of areas the USN has softened up on as of late like ASW (Building a whole slew of diesel and nuke subs) and AAW ( The possible purchase of Backfires coupled with the retirement of the F-14 which was specifically designed to deal with them). Also sheer numbers is of concern, if the chinese can crank out a whole bunch of relatively modern subs and the aegis-like destroyers, they could overwhelm the US in a battle at sea.
A link to a site that illustrates this-
http://usships.org