I'm assuming this is this gen only. And only going by games I've played for at least a few hours hence only a specific Uncharted, Gears of War, and Forza game.
Overrated:
Metal Gear Solid 4
Uncharted 2
Gears of War
Red Dead Redemption
Torchlight II
Call of Duty 4
LittleBigPlanet
Forza 2
Underrated:
Left 4 Dead
Vanquish
Bayonetta
Just Cause 2
Infamous
Valkyria Chronicles