Fallout 3 is more open and allows for more exploration. Fallout New Vegas was linear but with a better story. I was fast traveling back and forth to New Vegas every 5 seconds so I could complete a quest, where in Fallout 3 I would just wander out into the wasteland and hardly find the need to fast travel unless its to the opposite side of the map. The only reason I started a second playthrough of New Vegas was so I could get the hardcore trophy, which was the last one I needed.