I own a 2002 2500 HD Silverado 4x4 with the 6.0L engine that has 115000 miles on it for six years now and i could not be more pleased with it. I've done a few mods to it like larger tires, flowmaster cat back exhaust, K&N air filter and some other cosmetic items.The truck has been super reliable and is a blast to drive. As far as fuel economy, I didn't buy it for that. but It still gets about 16 mpg and tows anything i put behind it. As far as fuel economy is concerned 16 mpg from that big of a motor isn't that's bad. Their maybe more efficient trucks on the market today but I would still put my Silverado up against any gasoline truck out there as far as perfomance and reliability.
Favorite features, It's a Chevrolet of course. But anyway the power of the 6.0L engine is awesome and other than regular maintenance it's been great. The ride is awesome and handles like a much smaller truck, You can actually turn around in a parking lot unlike other 2500 trucks (Fords). It still has that old school look to it, it reminds me of the 72 chevy pickups. Plenty of room inside with the four doors, A full size person can be very comfortable in the back seat on extended drives and the kids love the room.
I really can't think of any improvements other than i wish i would have found one that didn't have all tan interior. Not that i don't like it, it's just a little blah. I've already changed some of the interior out for the black and plan on changing some more of it, But not all of it i like the two tone look inside the truck. It could have a roll down back window, That would be really nice in the summer when you don't feel like running the ac and just want some fresh air.