My vote goes to either Vagrant Story or Parasite Eve, both by SquareSoft. Both games are pretty short and I could see their stories being adapted into a 2 hour film without having to change all that much. Yeah I know Parasite Eve was originally a book and that book had a movie adaption, but I'm talking about the game's story here.
Mankind has been searching for the answer for decades. Actually Mortal Kombat 1 is imo the best movie adaptation out there. Which is funny because Paul W. S. Anderson has butchered everything else.