I dig the question. It's bringing out all kinds of interesting answers.
Among the most overrated players I think would be Pat Devlin, Matt Moore, Jorvorskie Lane, Daniel Thomas, Brian Hartline, Jon Martin, Dallas Thomas, Brandon Gibson, Jared Odrick (in current role), Vaughn Martin, Olivier Vernon, Jelani Jenkins, Jason Trusnik, Jamar Taylor, Richard Marshall, Dimitri Patterson and Chris Clemons.
Among the most underrated players I think would be Jonas Gray, Charles Clay, Rishard Matthews, Marcus Thigpen, Chad Bumphis, Michael Egnew, Josh Samuda, Jeff Adams, Derrick Shelby, Randy Starks, Koa Misi, Brent Grimes (if healthy), Nolan Carroll, John Denney and Brandon Fields.
Who the heck overrates backup defesnive lineman Vaughn Martin?