Suprised this thread wasn't brought up earlier. I've decided to jump into The Order:1886 fray!
If you ask me, I will go out on a limb here and say 2-4 Million Copies worldwide. If the reviews weren't so bad I would have said 4-7 Million. Bad reviews do tend to hurt the Legs of games in the longrun (Case in Point: Destiny).
Thoughts?