Truth be told, a movie like this should be pretty easy to make. Derailing an MGS plot is almost impossible considering the games are barely coherent themselves. A group of oddball enemies, a bunch of action sequences, a love interest, an absurd plot twist and a final battle against a mech involving a bazooka. Oh, and you have to have a cyber-ninja. Done deal, even Mr. Boll could pull this one off.
The only possible way I could see this movie being broken is if they play the "American action hero" card and have Snake run around waving the US flag while being overly patriotic. The "the world is a dick and everything is a conspiracy, no exceptions" rule is probably the only thing consistent about the MGS universe.