Gamasutra offers a comparative editorial discussing how New Vegas gives little feeling of satisfaction and accomplishment compared to Assassin's Creed: Brotherhood.
But even after the above-mentioned event that filled me with a new sense of purpose, there was still something that left me wanting, and I couldn't figure out what it was. That is, until I read an article from G. Christopher Williams on PopMatters.com entitled (Fallout, the 'To Do' List Simulator) that made me realize what was bugging me most: I never got anything done! I was apathetic because I never got a feeling of satisfaction or accomplishment. Even upon completing a mission, my quest queue was usually longer than when I started.
While I wanted to keep moving forward with New Vegas, I simply had to pick up and dive into some Assassin's Creed: Brotherhood as well. My plan was to check out Brotherhood for a couple hours then put it aside until I finished up New Vegas... But I didn't want to go back. When played back to back, these games shine an interesting light on each other, specifically on the biggest problem I have with New Vegas and one of the things I like most about Brotherhood.
I like the feeling of getting things done, and working towards a goal, and these are more satisfying in video games than they are in real life mostly due to their immediacy. As soon as I complete a quest I get money and items and experience, etc. In real life, rewards come at a significantly slower pace, and are rarely as materially satisfying as a shiny new sword.