The Mazda 6 is also known as the Mazda Atenza in Japan. Only models destined for sale in North America are built in Flat Rock - all other Mazda 6 cars for the rest of the world are built at a Mazda plant in Japan.
It's a great car - I drive one, and I have had it for nearly a year. It's a heck of a lot of fun to drive, well built, roomy inside, has a roomy trunk, and has good fuel economy, especially in the 4-cylinder versions. It also looks better than its competition, and is far more stylish than the bland 626 that it replaces. It is also available with a V6 engine coupled with a manual transmission, which sets it apart from many of its competitors.
The Mazda 6 is now also available in North America in 5-door hatchback and wagon forms - these body styles were available in Europe and Japan right from the launch of the 6/Atenza, but only became available in North America in February 2004. The 5-door hatchback (known as the Mazda 6 Sport) looks very similar to the sedan, and has no real competition in the North American market. The wagon (known as the Mazda 6 Sport Wagon) is very stylish for a wagon, and competes with such cars as the VW Passat wagon and the Chevrolet Malibu MAXX.