Can't wait to see what location they choose this time around. Would be cool to see NYC, Detroit, Dallas or some other large city. Hopefully with less wasted space and a good variety of locations to explore. Would also be cool to maybe get a mount/vehicle this time around. Vehicular/mounted combat would be amazing plus it makes no sense that there aren't functional cars or at least horses around anyways.
I loved both Fallout 3 and NV and sunk probably about 100 hours into each one not including the expansions which I have never really played aside from anchorage(which was crap

). It's really hard to say which I liked more. I love scavenging and large environments so both were right in my ball park, but I have to give the fun factor more to NV(after it got the insane bugs fixed on the PC version

).
I have never beaten NV though mainly because I love choices but hate choosing sides(especially when I have to weigh my options by who I hate the least) and being punished for choosing to go solo. Other then that I think NV had better combat, more interesting locations, better supporting characters(both in terms of story and ai), and an improved combat/loot system over 3.