7. Destroy All Humans
On paper, the idea of an alien invasion movie from the aliens point of view sounds golden. Then you realize that a movie about one alien invading wouldn't be as fun as a movie about dozens or hundreds of aliens invading, but adding more aliens would be a pretty big form of straying away from the original game in the first place. Then you realize that while the missions that poke fun at button down 1950's Americana are amusing, once the game play is removed they're nothing more than a running joke that wears thin kinda quickly. The thing that really helps to sink this ship, is the plot having the opposite problem of Xenogears. Once you remove all the bits with the player walking around doing things to further the overall mission, there's not a whole lot of story left to go around. It's just too short on it's own to be anything more than a half hour short film. So the only way to get this turned into a feature length flick would be to add a bunch of details and subplots that would alter the material beyond recognition or combine multiple games into one movie which would be very expensive for an untested property. Sadly the best thing that could happen with Destroy All Humans would be a movie that used the basic concept and ran with it in a new direction of it's own with a contract stipulating that EA's share of the profits would have to be used to fund the development of another game in the series from the same people who made the originals at Pandemic before they got bought out. The chances of something that sweet going down though... not as likely as humanity encountering real aliens.