ho... kay let's backtrack a bit
New Vegas approaches quest design and overall concept in a vein similar to the original Fallout games, and not Fallout 3.
Fallout 3 was a linear game at its core, it was a sandbox game, yeah, but the main quest was very weak, most sidequests completely generic, and the biggest area - the city of Washington - was a terrible disappointment. not to mention the whole eastern branch of the Brotherhood of Steel...
again, the engine doesn't make a game what it is, it's just a tool. if you think Fallout 3 is just as good or better than New Vegas, then we have nothing more to talk about, since our views are obviously very different