The mechanic used by Obsidian in FNV was very much an "ordinary" person in the wrong place at the wrong time. Now this person was not in an "ordinary" profession for the world, but hardly and extraordinary position either. Basically just a mailman shot and robbed for carrying a package someone else wanted. However, many people on various FNV boards complained that the character had really little motivation to get involved with the various factions. Frankly after getting revenge, there was little to drive the character forward in the narrative. In fact the one option the character did not have was to go back to doing his job as a courier. The one option most likely to be taken after the revenge motivation was played out. The courier really did not have a dog in the Legion/NCR fight.
I think the reason for this was, in part, because the character's possible companions had such shallow stories. The companion that has the most developed story also had little reason to be in the Legion/NCR fight.
So, if the game is going to try a story (as opposed to being a sandbox game) then the character being in the wrong place/wrong time meme has to have a good hook to propel the character forward into the story. I think this type of story be its vary nature has to have a "what's in it for me" type of angle.
In NWN2 by Obsidian, you have a similar type of story in that the player is really only special because he was in the wrong place at the wrong time (as an infant). Yet the character is propelled into the story because he becomes hunted, so survival becomes the motivation.
Of course in both FNV and NWN2, the character is ultimately disappointed at the end because the author's cheat the player of the 'reward'.
I agree with most of this post - FNV was especially relatable to me, though I did think Raul's afterstory was pretty awesome. After taking the wasteland for myself once, I then realized that I'd been shot in the head, left for dead, and aside from a few nice people in a village that's only suffered from proximity to Vegas, everyone had more or less been trying to make you sing and dance for them. Thus, I nuked them all. That said, I never really felt disappointed at the end of either of them - Mask of the Betrayer may have left me wondering a bit about my companions from the original campaign, but it was alright. F:NV took a bit more imagination, I'll admit, but the gamebryo engine can support some really neat mods.