BMW first earned its performance cred by dominating at the 12 Hours of Sebring in 1975. Just over 50 years later, the M2 CS is the ­current expression of that spirit. There are deeper BMW legends than the M2’s. The M1 was the first car to use the ­simple two-­character nomenclature in ’78, and the M3 has defined attainable and usable performance since the E30 version debuted in ’85. But in the 16 years since it appeared as the 1-series M Coupe, the M2 has adhered more closely than its siblings to the traits that made M cars icons. For one, BMW only just caved and introduced an all-wheel-drive option. And the M2 has a higher manual-­transmission take rate than the M3 and M4 combined. As those foundational M cars flounder, increasingly morphing into emotionless speed machines, the M2 shines as M’s enduring soul. With its wide fenders, naked carbon-fiber roof, and ducktail decklid spoiler, the M2 CS looks the part of a proper sports car, but as a supercar slayer, it’s still somehow a Q-...