I am genuinely shocked that I have never posted anything about Fallout 3 before this. Like a lot of my games I picked this one up way after it's release. I think I bought it about a year into it's life because I was never convinced that I would really enjoy a first-person RPG. I was very, very wrong.
I can't check right now what my official play time with this game was but I would put it at about 80 hours. There is just so much content in this game that it is crazy. I very much doubt that I have seen all there is to see. Those 80 hours were spread across about 18 months I'd say. I would play it a lot for short periods of time, get bored but would always come back to it.
There was a bonus to playing it late in it's life. There had been several patches for the PS3 version so I never encountered any significant bugs and all the DLC had been released. As as PS+ subscriber I got all the DLC for free. Some of it was poor like Mothership Zeta but some was very good like The Pitt and Point Lookout.
By the end I was throughly burnt out on the universe and I still have Fallout: New Vegas in shrink wrap. But it was one of the best games of this generation.