There has been talk for some time now about the possibility of a Half Life film being released in the future. A lot of fan films have been done already following the adventures of Gordon Freeman, such as this one:
One thing I feel is that if a Half Life movie were to come out, the setup for Half Life 2 (as opposed to the original game) would make for a much more interesting, story driven film. To me, the story in the first Half Life felt like more of an excuse to let you shoot at aliens, but the second game drew on some really interesting plot points from the likes of stories such as 1984 and Brazil, for example.
Though it came out after Half Life 2, a film that comes to mind when discussing the story of this game is Children of Men. Similarly to HL2, the population is unable to reproduce, though in this film it is because of a disease and not because of a suppresion field. There are also simliarities with the likes of an authoritarian government controlling the Earth's population, punishing people for even the most minor of infractions. Again, much like Half Life 2, a resistance movement crops up and fights against the antagonist.
It's a formula that seems to make for a great story - the suppressed masses rebelling against their oppressive overlords. I feel like if a Half Life movie were ever to be released, there could be a potential for a really awesome story that would go beyond action sequences and special effects, which to me, is what made Children of Men such a great movie.
Like Gordon Freeman, the protagonist in Children of Men is an everyman who gets caught up in a plot to rescue humanity. This is one of the things that, to me, makes Gordon Freeman such a neat protagonist. He isn't an action hero or a soldier, he's a scientist just trying to get through a day at work when this mess becomes his responsibility. I think that while the various fan films such as the one posted above are good, they focus almost too much on action sequences computer graphics. Oftentimes though, the best way to make something hit really close to home is to use less special effects. Doing this results in a very gritty, realistic looking film. Children of Men did this right, and some parts of this movie were enough to make you squeamish because of how real it seemed - much different than, say, a Michael Bay movie. Yes, brilliant CGI action sequences are impressive, but oftentimes it's so far fetched that it's hard to accept it as reality. Children of Men suspended my disbelief when watching it though.
I feel that if a Half Life movie were to be made, it should follow the formula of Children of Men - gritty, realistic, and story driven. If the story were to focus on the Half Life 1 narrative, it may come off as simply another haunted-house style movie, like Alien, for instance, which I don't have anything against... but I believe there is something quite special with the story presented in Half Life 2 - it has that dystopic/Orwellian/1984 aura about it, which is really quite immersive.
That is why it's my humble opinion that if they do make a Half Life movie, they should make it a Half Life 2 movie.