Yup after playing FNV some more it is a huuuuuge game. I'm barely even getting into all the different factions you can ally with. I'm trying to be a whore and whore myself out to every faction. I am by nature a quest whore. Some factions are exclusive but as long as you aren't too hated by them you can do quests for them.
I was even able to do some quests for the Khans in Red Rock Canyon. So many faction you can team up with which will make the end game interesting. Hopefully my actions affect the ending. I will be disappointed if that does not happen. Just some of the factions you can do quests for... NCR, Caesar's Legion (haven't actually done any for these guys), Followers of the Apocalypse, Brotherhood of Steel, Great Khans, the guys at Gamorrah Casino (you have your choice who to support), Yes man (I won't spoil his part in this), Head dude at Lucky 38 (I won't spoil his name), and then you have various towns and settlements you can do quests for and they all have their individual reputations. You might even be able to do quests for the Powder Gangers, I haven't tried.
This is a full game, make no mistake. It doesn't make radical changes to the system a la Civ3 to Civ4 or Civ4 to Civ5, but by RPG standards, it's an entirely new full game.