I just did the main quest and I finished the entire game in under 10 hours. I didn't realize the main quest was so short. There were only like 6 missions total, then it ends. I even did whatever random side quests I stumbled upon as well, although I didn't go out of my way to search for them or anything.
Not complaining, though. As I said, when I first played it a few years ago I got my fill of side quests. So this time I just wanted to rush through and finish it so I can play "New Vegas" (which is what I really wanted to play all along anyway).