The best replacement for fallout 3 is oblivion.

The best alternatives to fallout 3 are rated as following:
★★★★★  oblivion
★★★★★  new vegas
★★★  borderlands
★★★  skyrim
★★★  fallout new vegas
★★★  fallout 4
★  bioshock
★  fable 2
★  mass effect 2
★  mass effect
★  new vegas graphics
★  far cry 3
★  borderlands 2
★  new vegas map size
★  fallout nv
★  fallout 2
★  far cry 2
  nv
  bioshock infinite
  bioshock 2
  game of the year edition
  gears of war 2
  vegas
  fable 3
  fallout 3 new vegas
  new vegas size
  deus ex
  red dead redemption
  fallout 3 game of the year
  resistance 2
  fallout 3 goty
  halo 3
  dead space

Your alternative for fallout 3 is not listed? Suggest!
Speaking about fallout 3, one probably shouldn't forget about gfwl.

Other search terms related to fallout 3 and their ratings are:
★★★★★ gfwl
★★ graphics mods
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fallout 3
oblivion
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