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.
From what I understand, a lot of video game movies begin life as some other project a screenwriter was working on, but then the license gets thrown on afterwards. Then the director and writer end up begrudgingly and fruitlessly attempting to twist the video game's plot into the movie they actually wanted to make.
And the result is usually (1) unsatisfying to fans of the game because it departs too much from the original but (2) too video-gamey for mainstream audiences because of game-specific winks thrown in.
We're also seeing problems from parsing down a several-hour campaign (and possibly a multi-game franchise) into a two-hour coherent movie. The miniseries/serialized TV approach is probably a better medium -- see The Witcher.