I'll warn everyone looking for "cinematic" narration and linear plot - this is not a game for you. You'll be bored to death within the first three hours of play.
The rest - including myself - will be in heaven. Both the game itself and the main plot are very open. Almost every minute we have to take decisions that influence not only our fate, but also the balance of power in the area, the disposition of the local residents towards us and to the factions, relations between the factions, and even such things as store prices. Example? We help a local community maintain order, we choose one of the options, people are happy, they thank us, and then... the store owner raises all the prices by 50%. Well, the new authorities have him pay high taxes. And who will be affected in the end?
(...)
Our decisions are the essens of New Vegas. We really feel their weight and meaning here. It is very important to know the situation before taking them, and sometimes even guess what the consequences might be. The creators should be praised for not including any hints like "doing this quest will make group X hate you". We simply have to know the game's world. Without that, we can regret our choices quite often; especially that the interests of most factions (even the minor ones) most often clash. One of the things I love is that, keeping up with the Fallout tradition, there are no factions designated as clearly good or bad. They're grey, sometimes a darker or lighter shade, but never purely black or white.