When the Mercedes-Benz CLS-Class debuted for 2006, it shook the establishment with its four-door coupe designation. At the time, the oxymoron made as much sense as seeing "vegan veal" on a menu. But the concept has definitely caught on, as competing sedans with coupelike roof lines are becoming more and more commonplace. And it's easy to see why. The combination of a coupe's graceful, sweeping lines and the practicality of two extra doors holds specialized appeal.

As the progenitor of this composite coupe/sedan genre, the 2011 Mercedes-Benz CLS-Class is a great example of the advantages and drawbacks to this design. Most of the positive traits are related to styling, while the majority of its faults can be attributed to the compromises made in the name of style. As you can probably guess, the rear seat bears the brunt of this, with reduced headroom and difficult entry and egress.

The CLS has also typically offered more sporting driving dynamics than most of the other vehicles in the Mercedes lineup. But the company has made strides in designing its newest vehicles to be more dynamic, so the CLS no longer stands out in this regard. In addition, a redesigned 2012 model is waiting in the wings and will be introduced in May 2011. As expected, this next-generation car will be even more powerful and will refine the current car's attributes. Initial reports, however, note that rear headroom is still compromised.

For 2011, at least, there are a few other choices to think about if performance and dramatic styling are what you're after. The 2011 Porsche Panamera has a coupelike profile and very impressive performance, but it's more expensive and hampered by an overall look that's much more polarizing. You might also check out the 2011 Jaguar XF or XJ, both of which are sleekly styled and have plenty in the way of luxury and performance. But the CLS remains a pioneer for this class of car and is still worth consideration.

The 2011 Mercedes-Benz CLS-Class consists of two models: the CLS550 and CLS63 AMG.

Standard equipment on the base CLS550 includes 18-inch cast-aluminum wheels with high-performance tires, a sunroof, an auto-dimming driver-side mirror, automatic wipers, an adaptive air suspension, front and rear foglamps, cruise control, four-zone automatic climate control, a power tilt-and-telescoping steering wheel with shift paddles, 10-way power front seats with driver memory functions, leather upholstery, wood trim, Bluetooth, the COMAND electronics interface, a hard-drive-based navigation system with real-time traffic and a 13-speaker Harman Kardon stereo with a six-CD/DVD changer, satellite radio and HD radio.

The CLS63 AMG adds a more powerful V8, an AMG-tuned sport suspension, more powerful brakes, 19-inch wheels, more aggressive exterior styling, upgraded leather and faux suede upholstery, sport front seats and an iPod interface. Options exclusive to the CLS63 AMG include the AMG Performance package, which adds lightweight 19-inch forged-aluminum wheels, a limited-slip differential, track-calibrated suspension settings, a higher top speed (186 mph) and a sport steering wheel. The AMG Wheel and Sound package includes 19-inch forged light-alloy wheels and a 12-speaker, 705-watt Bang & Olufsen surround-sound audio system. Additional CLS63 options include interior trim that features carbon-fiber and faux suede.

The Premium 1 package is available on both models and includes adaptive bi-xenon headlamps with washers, a power trunk lid, keyless ignition/entry, a power rear sunshade, heated and ventilated front seats and an iPod interface (CLS550). Stand-alone options include 19-inch wheels, illuminated door sills, adaptive cruise control, and front and rear parking sensors.

The 2011 Mercedes-Benz CLS550 is powered by a 5.5-liter V8 that produces 382 horsepower and 391 pound-feet of torque. A seven-speed automatic transmission sends power to the rear wheels. Mercedes estimates the 0-60-mph sprint will take 5.4 seconds. EPA estimated fuel economy is 14 mpg city/21 mpg highway and 16 mpg combined.

The CLS63 AMG gets a 6.2-liter V8 that cranks out 507 hp and 465 lb-ft of torque. An AMG-tuned seven-speed automatic sends power to the rear wheels. In Edmunds performance testing, the CLS63 went from zero to 60 mph in 4.6 seconds. EPA estimated fuel economy is 12/18/14 mpg.

The 2011 Mercedes-Benz CLS-Class comes with antilock brakes, stability control, active front head restraints, a driver knee airbag, front and rear side airbags, side curtain airbags and the mbrace emergency telematics system. In Edmunds brake testing, the CLS63 came to a stop from 60 mph in 114 feet.

Though the 2011 Mercedes-Benz CLS550 is considered the base model CLS, its performance is far from pedestrian. The 382-hp V8 provides ample power and the car's handling is sharp without compromising ride quality. The CLS63 AMG, with its 6.2-liter V8, is geared toward the power-hungry enthusiast. It emits a seductive growl with every stomp of the accelerator and has higher handling limits thanks to its sport-tuned suspension. But you'll need to step up to the pricey AMG Performance package to approach the prowess of a Porsche Panamera.

While the CLS's graceful arching roof line certainly gives it a stylish coupelike silhouette, it's not without a few drawbacks. The lower rear roof line makes rear-seat access tricky for 6-footers. Once inside, those taller folks will find a noticeable lack of headroom, but there is plenty of knee and shoulder room. The short windows make the CLS's cabin feel less airy than a typical sedan's, but compared to a traditional coupe, the CLS is legitimately comfortable in back rather than merely passable. Also, trunk capacity is a useful 15.9 cubic feet.

Unlike newer Mercedes models with their austere, angular surfaces, the CLS's dashboard is curvaceous. Textures and materials are up to Mercedes' normally high standards. Most interior functions are controlled via Mercedes' COMAND interface; however, while this version features the latest software and menu structure, it's saddled with the previous generation's four directional arrow buttons instead of the multipurpose knob found in newer models.