I read The Mist before the movie was ever released, and I wouldn't call it "very different" from the theatrical version. I mean the plot and everything is the same, they changed some details, but you get the basic idea of everything that happened in the book. Even after reading it I'm not sure I'd relate it a whole lot to Half-Life. Sure it's got nasty tentacle monsters and stuff, which might have been the source of some inspiration, but 90% of the story has the main characters being trapped inside a grocery store. It's not what I'd call an actioner, it's mostly about interpersonal relations as people struggle to survive in a cramped area. A nearby military base is only hinted at, but the basic idea is that somebody there opened up a door to another dimension and now there are baddies flooding out. I guess you could call it Half-Life from another perspective, or something.
If you look around though, the whole setup is a pretty common thematic element in the science fiction/horror genre. Stephen King wrote another more recent book, From a Buick 8, which explored the idea of alternate dimensions in a way that I personally found more intriguing - and in some ways comparable to Half-Life.