What, not at all? But... it's a computer game. Surely the game bit is at least a teeny tiny bit important, otherwise why not just read a book or watch a movie? You'll find better stories there.
[Someone who thinks stories are of little consequence when it comes to judging a game's merits, and misses the days when the story of a game could be summed up with a sentence on the back of the box and would never deign to interfere with the actual game itself.]
Because, I like something called Plot and a little something called Original.
Movies nowadays = Twilight, OMAIGAWD
Books nowadays = Twilight, OMAIGAWD
@ Martyr: Fallout 3 is okay if you don't mind its not like fallout in many ways, And the story is horrible, But then again, this is my opinion, And alot of others probably share it too.
New Vegas is okay if you like Fallouts 'true' setting, And if you like the story, Though bugs can trouble some people, I don't mind them so much.