Just curious. For me, it would have to be the awesome dialogue and depth of conversations, like using Speech, Barter, Science, etc. I also love, like and absolutely hate certain NPCs and that's a lot more than I can say about other RPGs where I would only interact with the NPC for a quest or item. I actually have interest and want to interact with them. The world around me feels alive ( ironic for a wasteland, right? ) New Vegas would have to be my all time favorite game ever, flaws and all.