It's overall versatility.
The Avalanche was built on the Suburban platform and therefore is extremely comfortable, especially on long trips. It seats 4 comfortably and can squeeze 5 when required. It came with rear video entertainment with headphones which is good for families. The convertible bed is perfect for the DIYer who occasionally needs to transport plywood, studs, and even the occasional appliance or lawn mower. And the lockable/weatherproof bed cover allows secure transport of tools, groceries, etc. It handles well empty, loaded, and towing; and, the shift on the fly 4wd makes it great in the snow. The only complaint I have after 13 years is the poor gas mileage of the gasoline engine which was the only option. It would be 5+ stars with an economical diesel engine. Since they stopped manufacturing them, I will keep mine till the engine dies and then put in a modern diesel.