Finished Fallout 3 last night and used a few cheeky saves to check out a number of the endings (though I went for the generally godlike / pure / paladin route).
I won't spoil it, I quite enjoyed the ending but I get the feeling that if you don't spend lots of time exploring (I clocked about 54 hours of game time) you could probably run through the story in about 8 hours.
That said, as soon as I finished the story, I re-loaded a save game (keep some around handy just after you visit Eden) and continued the freeform gameplay (and picked up the DLC).
I Think I prefer the story arc to Fallout 3 than Fable 2, however they were both a little unfulfilling in the end, somewhat disappointing after my "last year" RPG having such an excellent story arc (Mass Effect). My reaction was probably because both Fallout 3 and Fable 2 allow you to inhabit a character and encourage exploration over narrative. Fallout seemed the more successful of the two games, though Fable made up for it by being very charming. In comparison, the Mass story was a strong one with the exploration, past the trivial no-planet planets, designed to drive the plot producing a feeling of much more cohesion.
I Still can't quite get in to Far Cry 2 though, I'm not sure why, the mechanics are solid, the story pretty random but it's just not really drawing me in (I guess that's what Zero Punctuations review said in a slightly more amusing manner). Just too serviceable to love.