Since 1973, the Buick Regal has taken the form of landau-roofed barge, square-jawed personal coupe, bad-___ muscle car, shark-nosed jellybean, forgettable sedan (more than once), and, as it sits in Buick showrooms today, Opel-derived near-luxury four-door. For 2012, the 270-hp Regal GS adds “competent sports sedan” to that list, and Buick wouldn’t mind if the [...]