411mania offers a pretty good interview with Fallout: New Vegas' project director J.E. Sawyer, asking for details on topics such as hardcore and the game's factions.
AL: By now, quite a few factions in the game have been revealed. How did you come up with what factions to use in the game, and were any left out that you wanted to put in?
JS: We knew initially that we wanted to revisit some of the classic Fallout and Fallout 2 factions like NCR and the Gun Runners, and I had always wanted to build up Caesar's Legion as a powerful slave army coming out of the east. After that, we looked at organizations that would be appropriate for the region given Vegas history. Factions like the Kings pay homage to Las Vegas' heavy association with Elvis Presley and the huge number of impersonators who live and work there. The Chairmen, who run The Tops casino, are inspired by the Rat Pack.
Honestly, there are so many factions in New Vegas that I can't say I regret leaving any out. I hope players will have a lot of fun interacting with all of the various groups in the Mojave Wasteland.
AL: It's been shown that the Nightkin are back in New Vegas. What made you bring these Super Mutants back, and have you brought back any other enemy types that were not seen in Fallout 3?
JS: I always thought Nightkin were underutilized in Fallout and seeing the Crimson Dragoons in the Fallout 3 DLC Operation: Anchorage made me think it would be pretty easy to use a similar cloaking effect for the Nightkin. I also wanted to explore the idea that extended Stealth Boy (the technology used for cloaking) use would eventually cause mental instability in the Nightkin after decades of use.
The most obvious enemies we've brought back are Geckos, the giant mutated lizards from Fallout 2. In their basic form, Geckos are small, funny-looking pests that don't pose much challenge for the player. Their larger kin, Golden Geckos and Fire Geckos, are much larger and more dangerous.