You can't really blame Mazda for following the trend. Most likely this is what the American consumers really want, whether you like it or not, for this segment since all other manufacturers are doing just the same - a big car. Some of the "negatives" of the previous model (justified or not) were the size and the power. Personally, I think the old Mazda6 was the perfect size for a mid-size car.
In my eyes, the new 6 has all the attributes to become the leader of the segment. The only possible negative I can think of right now is lesser fuel efficiency compared to the other V6s in the class (the I4 seems to be inline with the rest of the class or pretty close), but if you do the math, it all comes down to a few hundred bucks per year which is a rather small price to pay for the benefit of having a car you like to look at, sit in and drive every day versus a bland transportation appliance.