Well, I'm sure this will sound controversial to some, but I'm not a big fan of Metal Gear storylines. Sure, the gameplay is fantastic, but the kicker for me was the cutscene where Solid Snake is explaining the nature of reality to Raiden while standing in the middle of Wall Street in NYC. It was a load of pseudointellectual, meta-babble (not like the metal-babbles of Dragon Quest VIII).
Still, in competent hands, Metal Gear could probably be made into a fascinating film. If they made the movie in-house like Square did for Final Fantasy, it would probably feature all of that melodrama and Philosophy 101 bullsh*t that made Final Fantasy: The Spirits Within such a joy to watch, but a chore to listen to.
As for a movie I would like to have seen, I wish Lucas had adapted Knights of the Old Republic to the big screen. Instead, we got Jar-Jar and Mannequin Skywalker. The prequels were very much like sand.