Nothing; best car I ever owned.
I brought this Mazda 6 when it first came out. The car rides like a dream. There is not one problem wrong with it. I looked at the Acura TL, TSX, and I also looked at Toyota Camry, and the TSX is too small and noisy, and the Camry transmission liked to slip; and it's a brand new car!!
The Mazda 6 has more features than a Lexus, Hummer, and Mercedes put together! I love it so much for the full package; the sticker price was 21,240.
Best car ever!
You state that you like the car, which is fine, but you really don't give that much detail as to why you like it.