I personally have never owned one, but I know Mazda does manufacture, on their majority, good quality cars. And I've heard the Mazda 6 is indeed on par with its competition, the Camry, Accord, and Altima. So yes, it is a good car.
Mazda is the unknown gem of the auto industry. We are on our third one. A 3 this time. I don't know today's 6 but Mazdas are really very good cars. We had a 323 a while back that we gave to one of our sons with over 180,000 miles on it. 7 years later that car is still running...