Definitely Fallout 3. I have played over 200 total hours on that game (with the first four add-ons) and still haven't beaten it completely. Also, the soundtrack is purely amazing. The only real problem with it is that it's all single-player gaming and you only get to interact with NPCs and not actual humans.
[What a game you have horses in the place of dogs like your best friend? ] fable is best[/quote]Hey vermedosera, if you knew more about fallout3 you'll knew that you can have a dog companion called: Dogmeat, and btw there are no horses, lol