The 2012 Mercedes CLS is the second act of the car that invented both the market segment and the grammatical quandary known as the "four-door coupe." Made dramatically more bold for this go-round, it features an upright grille that flows back into a rump that disappears in photos but holds its own in person. The new sedan is also lighter, with aluminum doors that are 52 pounds less heavy and an aluminum hood, front fenders, trunk lid and parcel...