Just got back from seeing The Mist. It's always been one of my favourite Stephen King stories and I've been looking forward to the film for a long time. For the most part it didn't disappoint, though I did have some issues with the ending (more about that later).
Frank Darabont's screenplay stays very true to the novella for most of its running time. The setup (there's a storm, the mist rolls into town and a group of people are trapped inside a store with something horrible waiting for them outside) is handled very efficiently. There's plenty of humour in the film, which makes some of the plot absurdities easier to swallow.
When the creatures do start to appear, they're fairly successfully realised. The CG effects looks a little ropey in parts, but the prehistoric creatures from another dimension are pretty damn creepy (especially the spiders which burst out of their cocooned victims). As in the novella, the religious zealot Mrs. Carmody makes a very hissable villain who's even scarier than the monsters in some ways.
When the survivors finally leave the store for good, Darabont veers away from the novella and manages to give the film an ending that is somehow more hopeful and yet far bleaker than the original ending. I won't spoil it, but needless to say it will leave a bad taste in many viewer's mouths.
Despite that, this is definitely one of the more successful King adaptations in recent years (along with 1408, which has made this a good year for King fans). As he showed with The Shawshank Redemption and The Green Mile, Darabont is one of the few directors who really understands King's writing, and is able to transfer the author's voice to the screen intact. The acting is generally good - Thomas Jane makes his second appearance in a King film after Dreamcatcher and the supporting cast make their characters stand out. The film manages some impressively apocalyptic visuals with its low budget (I was especially happy to see the haunting image of the giant, Lovecraftian monster from the novella makes it into the film). I'd recommend the film to any monster movie fans. Just don't expect an upbeat Hollywood ending.