The Two Dead Girls:
Here King introduces us to the Green Mile, the death row of Cold Mountain Penitentiary in Alabama. He does a good job of setting up most of the later events. One exception: there are two passing allusions to the status of the narrator at the time of writing (he's no longer at the penitentiary). But they are embedded willy-nilly in the middle of unrelated paragraphs. If I didn't already know what was happening from watching the movie (edited), I'd have no idea what those asides meant. Whether I'd have stored them as potentially interesting anomalies or discarded them as sloppy writing, I can't say.
King has the ability to use language in clever ways. Unfortunately for the majority of the instances in this (and in later passages), he is seeking new ways to be crude or incorporate profanity. In fact, he uses profanity as though he thinks there isn't enough of it in the world and he's trying to convince us to make it more quotidian.
The Mouse on the Mile
Here he flat out tells you that the narrator is in an old folks' home, so that's out of the way. A lot of this chapter is about an unusual new arrival to the prison: a mouse with some special abilities. Unfortunately, the mouse doesn't seem to serve any real purpose except to fill up pages. His parlor tricks are just that—a parlor trick. In the context of a novel, this digression about the mouse might be okay—especially if it were spread out more. But as 3/4ths of a chapbook it's a complete distraction from the actual story line. It serves no purpose whatsoever.
King's prose is mostly pedestrian, but he seems to have dug out his thesaurus so that he could use every possible word for the male genitalia. His motive for doing this is that the narrator has a particularly nasty urinary tract infection. But despite his creativity at describing the afflicted organ, King can only come up with one simile for the pain caused by the affliction: coal oil set aflame. He uses that simile at least a dozen times in this section, and probably more.
He derides one of his characters: "Brad is a dimwit who thinks nothing is funny unless it's mean (used in the sense "unkind", "malicious")." Reworded a little, you see it for the dischism  it is: "Stephen King is a dimwit who thinks nothing is funny unless it is mean (in this case used in the sense "base", "crude")."
Enter the magical realism. King is known for writing horror, but this collection of chapbooks is best described as magical realism. Magical realism is fiction set in the real world but where magical or supernatural things take place and are also accepted as real.
So far I'm just trudging along. There's no hook that makes me want to keep reading; nothing to compel me to read the next chapter even though it's already 1 am. The best King can do is to dangle the "you won't believe what happens next!" carrot. Or sometimes he resorts to the maddening technique of having a character tell you they've found, learned, or realized something important, but he (King) refuses to tell you what it was for another several chapters. That doesn't create dramatic tension—that just annoys/angers the reader.
The Bad Death of Eduard Delacroix
Here King makes it clear that he disapproves of capital punishment. And he feels that people who are mean (e.g. Percy Whetmore, Brad Dolan) are worse than people who commit crimes (like rape and murder), but aren't mean. He later equates these mean people with Republicans by having one of the modern-day characters sport a bumper sticker that says, "I Have Seen God and His Name Is Newt Gingrich". Hopefully King doesn't think that being nasty like that (i.e. "mean") will win acolytes to his cause.
Here King starts drawing parallels between John Coffey and Jesus Christ (he suffers for others, he heals others' pain, he received an unfair trial, he is sentenced to die, (later) he punishes the wicked). He starts talking about Paul Edgecomb's "road to Damascus". He comes up with a bizarre explanation about why there is suffering in the world—not Satan (though Satan's real, too), but "a spirit of chaos".
Coffey on the Mile
Despite the allusions to Jesus Christ, King shows his disdain for organized religion by having Coffey refuse a preacher when it's time for him to "walk the mile". Earlier in the book he mockingly refers to Christianity (at least as practiced in Georgia) as "the Church of Praise the Lord Jesus Almighty".
As King ties up the 'novel', there were several things that were hard to believe. Paul Edgecomb is a prison guard in the South in the 1930s. There's no way he and his buddies would all be educated and enlightened enough to care about a black man they way they did. In another scene, with Paul and his friend, Elaine, intimidate one of the nursing home orderlies who is picking on them. I have trouble believing that people that old could pull that off.
My verdict: King seems to view the existence of capital punishment as one of the yet-to-be-eradicated blemishes of human nature. The electric chair, along with two human monsters, are the horrors of this novel. Yet he unintentionally deals with them by capital punishment (one is murdered and the other's mind is obliterated, which is essentially the same). And it is the compassionate and benevolent character, who is astonishingly capable of reducing human suffering, that destroys these two monsters. This is a glaring contradiction to the message King is trying to convey. And that's just sloppy writing.
The only thing that really made this different from the movie was the scene where Paul and his wife are in a car accident and Paul thinks that he sees John Coffey, but Coffey refuses to help. So, given the chance, I recommend you watch the edited version of The Green Mile and stay safely away from the stale source material.
 In actuality only one or two of the chapbooks had published by the time King finished the last one, so these advantages were obviated.
 See the Turkey City Primer.
 King does capture the spirit of the elderly by having Paul 'collect' the obituaries of all of his old acquaintances (I didn't really need to hear about it, though). King himself was only 49 at the time of writing, which is a little early for him to start. But his writing is definitely senescing.
 Other writing errors: he repeatedly uses the word "pop" when in Georgia the word most commonly used is "coke" (see http://en.wikipedia.org/wiki/Names for soft drinks#United States). He incorrectly uses the term pederasty to mean assault on young girls.
Old Sparky is by the NYS Department of Correctional Services, is in the public domain, and is available at http://en.wikipedia.org/wiki/File:Singchair.jpg.