All have different feeling to this and I can said I disagree with ya, greatly. AshJ list a handful but there a lot, lot more, but more in term in factions, location, and quest relation. That include the Boomers, 1st Recon, The whole Great Khans, The factions within New Vegas Casino, Fiends for christ sake, the Ghouls Cult, etc.
A world filled with supermutants, ghouls, mutated killer chameleons and talking robots just screams B-Movie to me.
And B Movies are great, except when they take themselves too seriously.
The mutants and ghouls in NV seems to have been shoved to the background, and the focus is on the humans. Which would have been fine if they weren't so darn normal. Normal people are boring.
The NCR in my opinion could have used a bit of Dr. Strangelove, while the Legion could have done with a touch of Monty Python.
And this is not the same with Fallout 3 because that is how I would view FO3 in that sense.