iv played fallout 3 all expansions maybe twice and watched my brother complete the main story and large secondary missions. as for fallout new vegas i bough all expansions but have only gotten maybe half way and havent played any expansions (bough the expansions while on sale in case i ever play it again) forgot why i stopped playing tho.
fallout 3 was one of my favorite games. the story was really nice, and exploration was pretty fun. (even tho now when i think of it the map is pretty small) i still remember when i was watching my brother play and he found his first laser pistol, we were pretty excited (i was 9 years old) fallout 3 was also our first rpg so that might be why its so memorable to me.
fallout NV was pretty nice too tho not as memorable. i did like the hardcore mode where there was hunger/thirst (the game was still to easy for me)
im not sure if ill ever play them again kinda moved towards skyrim. currently im modding skyrim for my first play through without cheats (the one i used cheats on i barely remember so this will be nice) just started installing mods today (having a hard time about what mods to install) really wished that skyrim was multiplayer, not like ESO tho. not much of a fan of those MMO rpgs (mostly like small group co-op)