i came to Under the Dome after being disappointed at the second episode of the show, so i started the audiobook and about 50 percent of the way through that, i started reading it proper. It was a true multimedia experience.
First thing though, i went in knowing the rough gist of the ending and I found that this did not ruin much for me. Getting there isn't half the fun in this case, it's all the fun. So if an ending can ruin something you enjoyed the other 99% of, you should sort of understand that the book is less about exploring "what caused the dome to trap this town?" than exploring "what happens after the dome goes down (and how)." Especially since, i think, the book allocates something like ten (disappointing) pages in total to fleshing out the "why" whereas it spends its other 99% dealing with the "what" and the "how."
So after watching and listening and reading, i think it's best to think of this book/story like a TV serial because King is actually really good at writing tv-style drama, down to the sort cheesy dialog, end-of-scene suspense and the instantly recognizable and memorable cast of new england townies. Each chapter has something between fifteen and twenty-five sections that simultaneously revolve around the chapter's major-arc and also serve to slightly advance the main plot. The book is something like twenty-five chapters long, so you can easily imagine treating it like a self-contained season-in-a-book. Or, i mean, a book.
The advantage the book has over the show (or almost any show) is that if you enjoy the first chapters, the writing doesn't really change much and the plotting remains consistent throughout. We don't get superfluous chapters dealing with some minor character's drug problem or 'a day at the hospital'/bottle episode or really any other season-filler-trope. Certainly there are chapters which heavily focus on 'one thing,' but these chapters also make up critical events in the course of the story.
Other reviews here point out how much of the ending is simply glossed over and that's true and distressing because so much of the book loves exploring incredibly brief events and traumas in stunning 120fps at 1080p.
It's implied that this brevity in explanation is due to the human inability to understand a deus-ex-machina and that, like most myths, the explanation is (probably) irrelevant. Should we really consider Zeus' motivations? Do they matter considering he's not usually the focus of any story? Those sorts of question are at the heart of whether or not you'll be bummed by the book's resolution (as it is). Are you more interested in the fate of the good people of Troy or are you more interested in why the gods magically mess with Achilles or Paris when it suits the story.
In contrast to contemporary TV plotting, the book doesn't have much by way of nonlinearity (ala flashforwords or chris nolanisms) and in a way that's great, but you start to think the book would have been better off being entirely bounded from the outset. Instead, it's not clear how long we're going to ride the chester's mill rollercoaster and so it's hard to calibrate our expectations for how meaningful any action is. Except you know that you're rapidly running out of pages. What do you make out of that situation? Suddenly two hundred pages to go, you end up in a horror novel where your sense of doom drives much of the suspense. There's a lot you get to see, but there's a loti> that you don't see and it really gets you thinking. Fifty pages to go and you start to believe anything could happen.
And then it's over.