I tried a small car and it just doesn't work for me. I wanted a big truck with the best mileage I could get and the Sierra Hybrid delivers big time! I am averaging between 20 - 21.5 MPG in the city and about the same on the highway. I have taken the family to the beach twice and it handles deep sand with no problems at all. The kids love all the room in the back seat. It is fun to drive. Drives really well on the interstate, plenty of power. Don't let the hybrid fool you. Had the vehicle for 3 months now and would buy it again today.
I love the folding mirrors (easy getting in and out of garage). The touch screen controls for XM are awesome - I didn't like satellite radio before with the little display screens. Of course the hybrid display is fun to watch too (my kids love it).
Not much really. A handle above the drivers door, place for sunglasses, one touch up/down for all windows, seat memory, etc. would be nice. For the same price as the Denali, they could these little features to really round out a great truck.