Fallout NV seemed like a "correct" fallout to me...
3 was too stripped and the plot was very "un-fallout". Siding with the BoS and having such a linear quest really killed it for me. To add to that...everything was just too destroyed for my taste. Sifting through countless rubble got old quick...the DC area was just rubble and more rubble followed by subway crawls. worst of all, it felt like a Fallout skinned FPS with light RPG elements.
It was good...but I felt NV really fixed it.
There are major different plot lines and factions, much more "RPG" elements and paths to take save just good-vs-bad karma choices. The exploration was also much more enjoyable. It felt like a fixed title rather than a cash grab...