Maybe my favorite ever?
I love this game and easily put in more than 200 hours on two long play-throughs. Some of the games haters can't get into the open structure of this, but to me this was its strength. There was enough motivation to explore and scavenge and while you're doing this, you stumble on a mission, or fantastic item, a difficult moral choice, or some hint of the past that fleshes out the world. Its a fascinating balance.
The DLC is also pretty solid, particularly Point Lookout which is very open structure like the main game. Other DLC tended to be more linear, more "shallow" but also fun nonetheless.
I'd put 6 stars up there if I could.