Have owned the Sierra for 8 months now and I really enjoy driving this truck.
I get pretty much 20-21 MPG regardless of city or highway driving.
On long stretches of country driving (45-50 MPH, no stopping) actually get about 26 MPG.
Just don't drive that way much.
Inside is big and comfortable.
My kids like it and so does my wife.
Black on black looks awesome.
It is fun to drive.
Pretty good in city traffic, awesome on the highway.
The truck is finished nicely (not like a luxury car), but very comfortable.