IGN lists off eight things in Obsidian's Fallout: New Vegas that would have made Black Isle Studios proud, including locations, companions, and quests.
The New Vegas Strip A well-intentioned piece but I'd argue there are things New Vegas does that make much more sense from a BIS perspective (more meaningful character builds, Vault 11) than the stuff they're listing.
Fallout 3 had nothing to rival Fallout 2's New Reno, but the New Vegas Strip is perhaps the most effective encapsulation of the Fallout aesthetic and ethos to be found in any of the games. The Lucky 38's Presidential Suite, made of faded leather and velvet and full of battered closets stocked with dirty pre-war apparel, is the physical embodiment of Fallout's decaying American dream. The strip itself, meanwhile, it a glitzy hellhole, full of desperate individuals with so little to live for that this strangled, neon-cast shadow of a once-great city is worth killing over. Shame you can't take a job as a fluffer, Reno-style. That's still probably the most degrading thing in videogames.
Drinking out of toilet bowls
Pretty much everything about Hardcore mode recalls Black Isle's Fallout games: the way your companions die, leaving you all alone out there in the wastes; the way a crippled limb or radiation poisoning can lead to a slow and inevitable death; the way everything in the entire wasteland, from the wildlife to the water, is trying to murder you. But there's nothing that depresses us quite so much as lapping irradiated liquid from a toilet bowl to stave off death by dehydration.