*** SPOILERS ***
Really easy 1000. My official game time was like 5 hours though that doesn't include a bunch of reloads. You could probably get the 1k in ten hours or less.
At the beginning of chapter 6 make sure to save your friend Pete. I didn't the first time and thought it was just a scripted part of the plot as that achievement is secret and he died right as I was at the button to save him.