well, a film is a directors interpretation of a story. there are no rules when making a film, no wrongs or rights. you just go ahead and make your film the way you like because it will never ruin what is already written. you can stick to the original plot all you like or you can steer off on a totally different tangent.
Plus, if you are directing a film based on a videogame you will have to change certain aspects in order to create tension filled and climatic scenes.
So whats your budget? $10million ish?