I just finished this game for the first time through yesterday and I plan on playing through it again. I have to say it is fucking awesome! As a fan of Fallout 3, I really liked this game. It was more like an enormous expansion pack with a totally new story, areas to explore, and things to do. They added a ton of new items, special ammo, perks, and dynamics to the game. For example, if you played Fallout 3 you'll remember the "karma" system. If you did good things you gained karma, and if you did bad things you lost karma. Well, in New Vegas you have the karma system, as well as a rating for each individual group there is in the game (if you help the good guys, the bad guys start to hate you etc). There are many groups you can help or hurt. Each with their own ways to benefit you later.
Overall, I found this game to be just as addicting as most of the multiplayer games I play! If you liked Fallout 3, you'll like this!