I'm not a huge fan of Stephen King novels being made into movies. I don't read a lot of King, but he generally writes too much stuff to stick into a 2-3 hour movie, so they more often than not get panned and end up being very empty and hard to follow.
One notable exception is Stand By Me, but that started out as a short story, not a full-sized King novel.
However, I did go to see it, and I have to say that it was a fun suspense flick. As such, there was some gore and it might not be a good choice for those with weak stomachs (although I'm sure that the teenagers will love it, if for no other reason than the fart jokes).
I won't explain the basic premise here because it was fun to watch it unfold throughout the film. The final understanding comes in the last scene of the film (although it is a bit heavy-handedly foreshadowed early on). Suffice it to say, there are good guys, bad guys and some innocent folks who are more difficult to figure out.
The film keeps pretty tight to a small number of active characters, which means you get to learn a little about each of them before the film is done. The main characters have all known each other since childhood and that provides some cute interactions that come from extensive shared experiences.
On balance, the film is quite suspenseful. We, as the audience, don't notice the 2:16 pass slowly, because Kasdan's screenplay (apparently significantly changed from the King original) keeps things moving quickly.
The acting was quite good, which I had expected and hoped. Morgan Freeman's character is quite different from most of the characters he has played recently, which is a fun departure for those of us who like to see actors stretch a bit.
If you don't handle gore well, you probably want to stay away from this one.