Well why do you see everyone saying the story was good?
Because they're loving stupid. Fallout 3's story was not good. At all. The part where you talk a 200 year old supercomputer to death just by saying "You suck" was the stupidest thing I had ever seen. At least, until the end when the Brotherhood of handouts and charity, who want to activate the water purifier, launches an assault on the Jefferson Memorial to prevent the Enclave from activating the purifier. Then Colonel Autumn, worst boss fight of all time, dies trying to prevent you from turning on the device he wants turned on. And then you go in and die because your robot/super mutant/ghoul buddy calls you a pansy and refuses to do it himself.
You can make arguments that Fallout 3's gameplay was fun, or say that you don't particularly care about story in a video game, and I'd admit that the Capital Wasteland was a neat environment to explore and that the DLCs for 3 were alright, but nobody can say the story was good. Because it wasn't.