I've owned my G6 3 years now. Purchased a fully-loaded GT with leather, panoramic roof, chrome wheels, etc. Closing in on 66k with nothing but routine maintenance. Daily driving is highway driving in Dallas rush hour 22 miles each way and average 29 mpg. Extended trips average 32 mpg as long as I stay below 70 mph. Panoramic roof is great in spring/fall.
Great gas mileage and roof. Multi- function key fob lets me start car before I get there.