When it went on sale in the United States in 2005, the E-class–based CLS popularized the “four-door coupe” shape via a plunging roofline and a slim greenhouse, and would earn 40,000 sales in the U.S. over the next five years. It also spawned a number of copycat designs such as the Audi A7, the Volkswagen CC, and the Jaguar XF.

The second-generation CLS, which goes on sale here early next summer as a 2012 model, isn’t as pretty as the first one. The new body is a mixture of unimpeachable proportions and jarring design details. The overall envelope is elegant, but Mercedes embroiders it with brash details such as aggressive air scoops around the front bumper and sharp creases along the flanks.

As with virtually every car that comes to market these days, the CLS is bigger than the vehicle it replaces. The wheelbase has grown from 112.4 inches to 113.2, and the overall length is now 194.5 inches, up from 193.6. The car is slightly taller and wider, at 55.8 and 74.1 inches, respectively. The running gear comes from the new E-class sedan, but the CLS has a slightly wider track in front and back.

Although it’s still a striking car, the CLS places equal emphasis on its bevy of safety features. There are nine standard airbags and no fewer than 12 assistance systems. New among these are three active systems to help with parking, staying in the appropriate lane, and monitoring blind spots. The ­latter doesn’t merely alert a driver to a car in a blind spot; it uses the brakes to tug the CLS away from an approaching vehicle.

More important to enthusiasts, Mercedes is using its new 4.7-liter, direct-injection twin-turbo V-8 in place of a naturally aspirated 5.5-liter engine. (It seems that Mercedes’ naming conventions have followed BMW’s lead, in that they tell you ­absolutely nothing about what’s underhood.) This engine made its debut in the CL550, where it was rated at 429 horsepower. In the CLS, the power is down to 402, although that’s still 20 more horses than in the previous CLS550. The old engine made 391 pound-feet of torque, which grows here to 443, available from 1600 rpm.

Mercedes claims the twin-turbo engine is 10 to 15 percent more fuel efficient, thanks to the smaller displacement, direct injection, and a stop-start system that will not come to the U.S. on this engine, instead waiting to appear on the upcoming AMG model. The engine is mated to a seven-speed automatic transmission, and all-wheel drive will be available later. Performance should remain similar to that of the previous model; the last CLS550 we tested managed the 0-to-60-mph sprint in 4.7 seconds. But by  the middle of next year when the car launches here, it’s likely that Mercedes also will introduce the CLS63 with a twin-turbo 5.5-liter V-8 making about 550 horsepower.

Compared with the previous model, the new CLS interior provides a little more shoulder room (up by 0.9 and 0.5 inch, front and rear), thanks to slimmer door trim. The interior quality is also better, with actual metal rather than plastic on some of the switches, real wood panels, and gorgeous, thick leather. The old, fiddly COMAND ­system used to access the navigation, audio, and telematics is gone, replaced by an iDrive-style controller. Overall, the quality and ambience come close to those of the S-class.

Over the road, the CLS550 provides something similar to the E550 experience—which is to say, biased toward luxury rather than sport. The engine sounds good, but it’s very muted, and under full throttle the V-8 growl fades beneath a blanket of turbo whoosh. The power delivery is sensational, though, with no perceptible turbo lag.

The air suspension and continuously variable damping combine for a plush highway ride. Ultimately, however, it lacks a convincing degree of athleticism: Though precise and linear, the new electric power steering provides far more feedback than does the chassis, which is pretty inert.

The CLS is still an expressive machine, and it remains a stylish alternative to an E550 sedan. We just wish it had a little more fire. Perhaps the upcoming CLS63 AMG will satisfy  that desire.