Somebody once said to me that people seem to really really like whatever of the two they play first, and then they are either impartial or dislike whichever they play next... Not sure how much truth there is to that though - personally I liked FO3 a lot but could immediately see that NV was very much an improved version and more-of-the-same
Yeah I found that NV felt very much the same, but I did not get as hooked on the story and just didn't like the map/atmosphere as much...
That's probably a fair statement as they are very similar gameplay wise.