The biggest problem about New Vegas is not having memorable moment. Fallout 3, on the other hand, has so many moment like the antagonizer, the crazy tree lover, the people who believe radiation can cleanse our body, a town rules by children, the rich people, the naughty nightwear robber, vampire, a lady who collects nothing by cola, and etc
For New Vegas, other than their belief system differs, there isn't really much of a fascinating world