Fallout 3 is a game you love to hate, simply because it isn't a bad game per say. But it'll give you such a headache in terms of bugs, crashes and that isn't taking into account mods. Even the pure vanilla FO3 experience has an absurd amount of bugs and problems which are only compounded by modding the game, and everyone will say that these Bethesda open world RPGS are made to be modded and playing vanilla just isn't fun, but be prepared for even more issues as soon as you start popping in those extra textures, new weapons etc -
My biggest beef isn't really with FO3 per say, but more with the DLC content especially operation anchorage which is dreadfully buggy and having mods can totally break it, the wiki page clearly states in a massive wall of text how many issues this particular DLC contains, and for some reasons..was never fixed properly.
Unfortunately Bethesda are known for releasing unfinished or seriously buggy games and sadly, FO3 is a prime example especially considering its age now. Most new-comers to FO3 will most likely pick this game up via steam sales etc and will quickly discover how great, and how terrible Fallout 3 can be.
I honestly think 6 is a fair score considering the sheer amount of bugs which was never fixed or just simply ignored couple that with the near hourly CTD problems the game can have. I would have personally given Fallout 3 a score of 9 if it wasn't for all the major issues, but that being said - anyone who likes open world rpgs will definitely get some enjoyment (and frustration) out of this game.