Purchased my Avalanche in late 2007 as a replacement for my 2000 Silverado Extended Cab. I wasn't sold on the the previous years Avalanches, as they appeared to be "cheaply" made. My wife liked the Avalanche and convinced me to give up my practical pick-up for a vehicle that would accomodate our 3 kids, yet still offer the functionality that I required (pick-up bed). I've been more than pleasantly surprised. It rides terrific. I own a contracting business and tow a large boat. The Avalanche hauls and tows large loads with no problem while maintaining considerable interior luxury. I highly recommend the navigation system. Additionally, I recommend the DVD player if you have kids.
Chevy spared no expense in designing the interior of the Avalanche LTZ. It looks and feels like a luxury automobile. The DVD player, camera and reverse sensors are great if you have kids. The camera also make hooking to trailers a snap.
Just as most everyone else has indicated, better mileage would be a plus, although the Avalanche, with its, multi-displacement enging, gets better mileage than my previous Silverado. An efficient hybrid Avalanche that offered as much power would be a plus.