Mythology is filled with half-this, half-that creatures. A griffin is half eagle, half lion. A mermaid is half fish, half hot babe. More recently, Robocop is half robot, half cop. The 2010 Mercedes-Benz CLS-Class follows this grand tradition: a so-called four-door coupe that blends the sleek lines of a graceful grand touring two-door with a dose of four-door practicality.

There may be nothing mythical about the CLS, but this half-sedan, half-coupe creature has established a pretty grand tradition of its own, as demonstrated by copycat models like the Volkswagen CC. Car designers and car buyers alike have embraced the concept of a sedan that sacrifices some functionality -- especially in the backseat -- for a whole lot of style.

The CLS started life back in 2006 as the previous-generation E-Class. While the designers went to work on that sexy styling, the engineers were busy making it a more sharply tuned driving machine. Then the AMG division added its usual magic with the CLS63, a thrilling super sedan with 507 horsepower that hits 60 mph in a scant 4.6 seconds. The result is a car that not only looks different from the rest of Mercedes' sedan lineup but drives differently, too.

Indeed, the CLS is generally more fun and involving than the typical Mercedes four-door, with a greater emphasis placed on driving enjoyment -- though the new AMG C-Class and E-Class models have certainly closed the gap in this regard. Even the base V8 engine provides more than enough thrust to make freeway entrance ramps and passing maneuvers simple affairs.

Those aforementioned practicality sacrifices can't be ignored, however. Headroom is significantly less than in the E-Class -- especially in the two-person backseat -- while visibility is hampered by the steeply raked windshield and short side windows. Getting in and out can also be difficult, depending on your agility level. Another issue is that the aging CLS is missing a few advancements from more recent Benz models, such as the latest COMAND electronic interface and the slick new torque converter-less AMG automatic transmission from the E63 and SL63.

Because it's such an odd creature, there are few apples-to-apples competitors for the 2010 Mercedes-Benz CLS. The Porsche Panamera is a similarly conceived car that's better in many ways, but you'd better be prepared to pay for it. The Jaguar XF is more of a traditional sedan, but its styling was inspired by the CLS, and it's significantly cheaper than the Benz while giving up little in the way of performance or luxury. Mercedes' own E-Class and the BMW 5 Series are also worth considering, especially since they, too, are less expensive. But the 2010 Mercedes CLS-Class remains a special car, and like other mythical half-breeds, it will likely be remembered for a very long time.

The 2010 Mercedes-Benz CLS-Class consists of the CLS550 and CLS63 AMG. Standard equipment on the base CLS550 includes 18-inch alloy wheels with performance tires, a sunroof, an auto-dimming left-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, 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 memory-card slot and a 13-speaker Harman Kardon stereo with a six-CD/DVD changer, satellite radio and HD Radio. The Sport package adds 18-inch AMG wheels, high-performance tires, more aggressive exterior styling cues and a sport steering wheel with black shift paddles. The Sport Package Plus is the same but includes 19-inch AMG wheels. A wood-trimmed steering wheel and shift knob are also available.

The CLS63 AMG adds a more powerful hand-built V8, an AMG-tuned sport suspension, AMG brakes, 19-inch AMG wheels, more aggressive exterior styling, upgraded leather and faux suede upholstery, sport front seats and an iPod interface. The AMG Performance package adds lighter-weight 19-inch alloys, upgraded brakes, a limited-slip differential, track-calibrated suspension settings, a higher top speed and a leather and Alcantara sport steering wheel. The AMG Wheel and Sound Enhancement package includes 19-inch forged light-alloy wheels and a 705-watt Bang & Olufsen surround-sound audio system. Additional CLS63 options include carbon fiber and Alcantara interior trim.

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

The CLS550 gets a 5.5-liter V8 that produces 382 hp 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.

The 2010 Mercedes-Benz CLS-Class comes with antilock brakes, stability control, active front head restraints, a driver knee airbag, front and rear side airbags and side curtain airbags. In Edmunds brake testing, the CLS63 came to a stop from 60 mph in 114 feet.

In addition to offering prodigious thrust from its 382-hp V8, the 2010 Mercedes-Benz CLS550 makes a good showing when the road turns curvy. Left in its default "Comfort" mode, the standard adaptive air suspension provides handling stability as well as a supple ride over bumps. The two Sport settings facilitate more aggressive driving without overly compromising Mercedes' typical refined ride quality.

The CLS63 AMG is a real hoot thanks to the vicious thrust of its 6.2-liter V8 and the seductive growl it emits with every stomp of the accelerator. Its sport suspension and brakes push the handling envelope even further, though you'll need to step up to the pricey AMG Performance package to approach the prowess of a BMW M5 or Porsche Panamera.

The CLS's coupelike body style makes getting into the rear compartment tricky for 6-footers. Once inside, those taller folks will likely hit their heads on the roof, but there's 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.