Originally Posted by PenderPowguin
What difficult setting were you on? You made sure to have hardcore on before you left the Doc's house right? I haven't tried it out myself but perhaps you do need to complete every mission? But at the same time I dunno why, I got The went that away achievement just by walking into the Vegas strip so perhaps it's a different factor?
When it asks you for the first time if you want to play on hardcore mode say yes, if you dont you cannot unlock the achievement. Also once you have it on hardcore people seem to be having issues unlocking the achievement but they have also stated they changed the difficulty, but still left hardcore on so the best thing to do there is NOT change the difficulty...
Also you dont need to do every mission, just the main story missions, i accomplished my rush through in 5 hours, its really not terribly difficult.
sorry for so many posts in a row, just trying to help where i can!