Sometimes you shouldn't get what you wish for.
The Mist is one of those pivotal and deeply inspirational stories for me (Lovecraft's the Colour out of Space, is another). I read Stephen King's novella when I was sixteen, and it crouched in my brain and laid eggs there. There was an intimacy in that story, in the face of the inconceivably awful, that I found utterly compelling, and I'd always wondered what it would be like as a movie.
Well, the Mist is a fine movie, but the inconceivable is now conceivable*, and I kind of wish that I hadn't seen it.
Well, too late for that. Still, if you didn't fall in love with the novella when you were a wee nip, I reckon there's a lot to enjoy here, and if you did, well, maybe you'll be better at separating the two mediums.
*I kind of wonder if the person that designed the giant monster at the end of this movie was the same person that designed the monster in Cloverfield - a movie that had the advantage of not being based on a beloved childhood tale.