The toughest gig in town? If you're a mainstream automaker, it's the midsize sedan segment, now the absolute heartland of the American new car market. Last year's Motor Trend Car of the Year set benchmarks for ride, handling, interior package, and powertrain in the segment. The Camry sales juggernaut just keeps on rolling, a testament to Toyota's massive marketing muscle and consumer inertia, and the Hyundai Sonata has everyone worried about the growing reach of the Koreans. And just to make things even more interesting, in the past few months alone, Chevy launched a new Malibu, Honda a new Accord, Nissan a new Altima, and Ford a new Fusion. If you're thinking of crashing this party, you'd better bring your A-game.

Enter the 2014 Mazda6.

Mazda is a car company in transition. For more than 30 years, it operated in partnership with Ford Motor Company, which at one time owned a third of the Hiroshima-based automaker. Ford's involvement was a blessing and a curse: It gave relatively small Mazda a big brother it could lean on for everything from R&D to vehicle architectures to manufacturing plants, though it also meant Mazda had to conform to Dearborn's view of the automotive universe. No longer. Since 2010, Mazda has been free to pursue its own destiny. But as a company that last year sold about 1.3 million vehicles worldwide, that freedom has necessarily been tempered by the need to watch the pennies. Put simply, Mazda can't afford to screw up.

Yep, there's a lot riding on the all-new Mazda6. This is perhaps the single most important new vehicle Mazda will launch this side of the next-gen Miata, the company's touchstone car. The good news is that, at first blush, Mazda looks to have got a lot right with the new 6. In terms of the current crop of mid-size sedans swarming like frenzied piranha around the American consumer, it looks to be an A-game car.

The new Mazda6 is the second car designed from the wheels up to make the most of Mazda's Skyactiv suite of fuel-saving technologies. It shares engines, transmissions, and even some structural elements - the front and rear subframes, for example - with the CX5, which was the first completely new Mazda the company launched since the 1967 Cosmo Sport. Among the changes made to CX5-shared hardware are a revised front strut layout to improve steering smoothness, revised brake booster characteristics for better initial pedal feel, and a reprofiled steering knuckle neck to reduce road noise.

Built in Japan at Mazda's Hofu plant, the 2014 Mazda6 comes in two bodystyles -- sedan and wagon -- with a choice of five different four-cylinder engine variants -- a 2.0-liter gas and 2.2-liter turbodiesel, each available in high or low power tune, and a 2.5-liter gas model -- plus the choice of six-speed manual and automatic transmissions. U.S. buyers won't have to spend a lot of time deciding which Mazda6 they want when the car goes on sale in January. The sedan with the top-of-the-range 189-hp, 2.5-liter direct-injection Skyactiv-G engine mated to the six-speed automatic transmission is, for now, the only model headed stateside, though Mazda USA officials won't rule out considering additional variants. Simple market dynamics suggest they have to: All the other key players in the segment offer a number of engine and transmission variants.

The Mazda6 projects a commanding presence on the road; unlike, say, Ford's new Fusion, it doesn't look smaller than it really is. Styled under the direction of Akira Tamatani, the man responsible for the Takeri concept sedan unveiled at the 2011 Tokyo Show, the new Mazda6 boasts a unique "cab-rear" proportion that makes it look more like a rear-drive car. Extend a line from the point where the A-pillar meets the front fender on most front-drive cars, and it will invariably run through the front axle centerline. On the Mazda6, however, the A-pillar touchdown point has been moved rearwards almost four inches compared with the outgoing model, visually moving the front wheels forward compared with the greenhouse. With a typical Japanese anime flourish, Tamatani-san says it makes the Mazda6 look like "a wild animal ready to leap forward at any second." We wouldn't go that far, but it is certainly a handsome, athletic-looking car.

Curiously, the Mazda6 is the only midsize car in the world where the wagon version is built on a shorter wheelbase -- 80mm shorter, to be precise -- than the sedan. The reason, says Mazda6 program manager Hiroshi Kajiyama, is the four-door has been optimized for the U.S. and China, where consumers prefer their midsize sedans on the larger side, while the rakish wagon is aimed at European buyers, who have developed a fondness for sporty load-haulers. The sedan's wheelbase is a generous 111.4 inches and overall length is 191.5 inches, making the Mazda6 one of larger cars in the class. That long wheelbase, coupled the 72.4-inch overall width, make for a decent cabin with good rear seat accommodation for adult passengers. Moving the cabin back from the front wheels also means the front wheel housings are less intrusive, allowing Mazda to push the pedals outwards and more in line with the driver's body.

There's a lot of black plastic inside the Mazda6 -- you can have any interior color you want as long as it's black, or black with off-white seat facings and door trim patches -- but it's well-executed and devoid of any gratuitous design gimmickry. The center stack features simple rotary dials for the HVAC, and a 5.8-inch nav screen sits in a nicely scalloped recess adjacent to the simple three-dial instrument cluster, the right-hand dial of which is a 3.5-inch multi-function display. An MMI-style rotary dial and menu button cluster on the center console control all the nav-screen functions. Only little telltales like the warm-to-the-touch aluminum accents (which means they're actually plastic) and the cheap-looking graphics on the display screens (the nav system is TomTom-based and looks vaguely aftermarket, though it is updatable) remind you you're in a mainstream sedan.

One new technology debuting on the Mazda6 is Mazda's i-ELOOP brake energy regeneration system. Loopy name aside (really, can we stop with the Apple rip-offs already?), it's a clever system that combines a variable voltage alternator with a low-resistance, high-discharge double layer capacitor and DC/DC converter to quickly harvest energy during deceleration periods as short as 7 to 10 seconds. The capacitor sends the harvested energy to the DC/DC converter, which then uses it to power all the car's electrical systems. Surplus energy is sent to the regular battery. Shin Okamoto, who heads Mazda's Drivability & Environmental Performance Development Department, says the capacitor can store enough energy to power the Mazda6's myriad electrical systems for one minute. The genius behind this system is the capacitor enables the fast charge/discharge cycle that would otherwise damage a regular battery.

So, how does the 2014 Mazda6 drive? Pretty nicely, at least for the 70-odd miles we covered on French roads in pre-production Euro-spec cars. As promised, the steering feels nicely linear, and provides decent feedback. The chassis is balanced and composed, and while the ride is on the firm side, it's never flinty, with impact harshness and road noise very well-suppressed. The 2.5-liter Skyactiv four makes its presence heard when you hit the gas pedal, though it's never harsh, and, despite a slight deficit of mid-range torque, it's a willing worker. The six-speed automatic shifts quickly and crisply, and the early lock-up of the torque converter in each ratio not only helps gas mileage, but also throttle response. In manual mode, it responds promptly to commands from the steering wheel-mounted paddle shifters. If you desire even a modicum of driving enjoyment from your midsize sedan, this transmission alone is a major reason to buy the Mazda6 over a new Honda Accord or Nissan Altima and their soggy CVTs, or the new Ford Fusion or Chevy Malibu and their stubbornly unresponsive autos.

While in France, we also got the chance to sample a Mazda6 with a high-power version of the Skyactiv-D 2.2-liter turbodiesel (173 hp versus 147 hp) mated to the six-speed auto. Here's another curiosity: Central to the Skyactiv story in the gasoline engines is their ultra-high compression ratios of 14:1 in the 2.0-liter engine and 13:1 in the 2.5-liter. But for the Skyactiv-D Mazda boasts an ultra-low - for a diesel - compression ratio of... 14:1! The lower compression ratio allows for lighter components, which means the engine will rev to 5200rpm, and Mazda solves the cold-start inefficiency problem by recycling exhaust gases to quickly heat the combustion chambers. More importantly, though, the engine's low NOx emissions mean it would not need expensive urea after-treatment to be 50-state legal in the U.S.

It's a real sweetheart, the Mazda6 diesel. Ride, handling, and steering are the same pleasant mix as in the 2.5-liter Skyactiv-G car, with the added benefit of 64 percent more torque. Sure, the little tingles through the steering wheel and the floor at idle leave no doubt you're driving a diesel, but once underway, everything settles down to a muted oily growl that's less intrusive than the gasoline engine's gargly snarl. The more powerful 2.5-liter is faster to 60 mph and over the quarter mile, but the smaller diesel feels quicker; it punches out of corners harder and is more alert on the freeway, with the six-speed auto adroitly exploiting the meaty 420Nm on tap from just 2000 rpm. Put simply, the diesel's more fun to drive, and you'll use 24 percent less fuel into the bargain, according to the Euro Combined Cycle fuel economy numbers.

If Mazda USA really wants to stir up the mid-sized sedan segment, the Mazda6 diesel is a no-brainer.