Quite possible: NONE. Games just don't work as films. Take Silent Hill - the film. Now, I love the silent hill series (although the 4th wasn't as good as the rest, and I think Silent Hill 5 will suck because it's not being made by the original team behind the first 4 games), but the film was really bad. Why? Silent Hill was scary because YOU were playing the character, walking around the deserted town, seeing all the weird monsters, YOU had to fight them, solve the puzzles, and survive the nightmare. The silent hill games were scary because it was about YOU playing the game.
The Silent Hill film just had actors (bad ones at that), running around, and it didn't feel scary in the slightest, because you knew it was the ACTORS that were doing stuff, not YOU. Thus, the Silent Hill movie failed.
This is why games don't make good films - games are (usually) about YOU being immersed in the experience. Films are about TELLING you the experience or showing you the experience.
Also, films are restricted to about 3 hours, 4 at most. It's too short a time period to do the story justice. Silent Hill thew out most of the story line from the games and put in a pretty crappy one instead.
I can't imagine a Metal Gear film that could properly implement the plot. I can't imagine a Halo film being any good - you wouldn't play as master chief gunning down aliens (which is fun), but you'd just WATCH an actor PLAYING as Master Chief (probably badly too), gunning down aliens (which would be boring). It's fun to mow down wave after wave of enemies - it forces to you react, to dodge, to reload, etc. It's really boring to WATCH an actor mow down wave after wave of enemies. Really boring in fact.
Games do not make good films. They are two different forms of entertainment, and they can't be meshed so easily.