The ending ... redux
Endless comments pro & con have been expended over the Darabont's ending to The Mist. Personally I favor King's original ending, & I'm suspicious about his suggestion that he wished he'd thought of it himself.
Here's why ... King's original ending—suggesting that the mist, & what it brings, extends indefinitely—places the story firmly within the realm of cosmic horror, a genre with which King has explored in It, The Langoliers, N, Crouch End & a few others. Most successfully, I might add.
Darabont's ending changes it altogether, from cosmic horror to BEM. After all, some of that genre's conventions hold that the monsters are finite in scope, as was Darabont's mist; and they are usually destroyed in the end. The finale is typically a return to normality—not quite the case in The Mist, at least not for the protagonist. But for everyone else.
So it's not just the ending that's changed here, but the entire genre the story occupies.