It is sad that there is no reminder in FoNV, that the founders of the NCR and the founders of the khans all came from the same vault. (so has the Vipers & Jackalls)
It definitally add a layer in their eternal conflict.
My favorite faction of the franchise remains the unity, but they are so scatered in FoNV that i wouldn't call them a faction any more.
But it was great to see how their renmants evolved. Same for Khans/BOS/Enclave renmants.
About new factions, i grew fond of the kings.
I was never interested in the real star whom they don't know the name, but i think the value they intend to follow are touching.
Beside that, Freeside is my favorite location post-Fo2. It really give the feeling of a post-war big city outskirt, with all the people attracted by the light of the strip, but put aside by its leaders, and left to handle themselves.
On the other hand, i was a bit disapointed by the Boomers. They are not an awfull context, but i think they give them a too important role for a not so interesting faction.