
The first pack will hit in January, and will be called Operation: Anchorage. It'll let you enter a military simulation and re-enact the battle between the US and the Chinese--this is one of the key pre-vault struggles in the Fallout universe, which is kind of cool.
The Pitt will be released in February and will have players travel to Pittsburgh, which is now a town full of raiders.
March will bring the Broken Steel pack, which picks up after the completion of the game's main quest and has you join up with the Brotherhood of Steel to eradicate the Enclave forces from the Capital Wasteland.
Continuing the story seems interesting. But if you want to continue the story yourself, you'll also be able to build your own content in the PC version via mod tools to be released in December. That should really jump start the Fallout 3 mod scene, which has been limited to pretty basic changes so far.