Curiosity compels you to read this!
THE DEVIL IS IN THE DETAILS
It was kinda hard to decide the rating on this novel.
If I'd think only on the raw reading experience, I would say that it was a 3-star material.
However, I had to ponder about the whole additional info and further development of characters compared with my experience with the film adaptation (which certainly is one of my favorite horror films). So, I think that the fairest rating is giving a solid 4-star rating.
Certainly due all those deeper details in the original book, I think that novel & movie make an irresistible combo to do.
You watched the film, and then you'll appreciate even more the extended information that you'll find in the original novel, but in matters of frightening, well the movie has a clear advantage, but don't dismiss the novel so quickly.
Since, may be not the best horror novel that I've ever read,...
...but certainly the book has...
...something to compel you to read it, and have it a huge respect to it.
MOVIE V. BOOK: DAWN OF POSSESSION
I am not surprised if almost any reader has watched the film before reading the novel..
...And my case wasn't any different.
I have watched the three film versions: Original theatrical, "The Never-Before-Seen" version and the "Extended Director's Cut". Any comment that I'd make in this review about the film adaptation it will be based on the latest mentioned version, the "Extended Director's Cut", due it's the most complete and also it's the one that I have on Blu-ray so it's the one that I have more fresh on my mind.
It's interesting how the film is generally accepted as the most terrifying movie of all time, while the novel doesn't keep that distinction. Actually the debate about which novel is the most terrifying of all, it's an endless dispute that I'm sure the general reading community never would be able to agree in a specific novel.
While the imagination is the best special effects generator, I have to admit that it wasn't so shocking to read scenes than in the visual presentation where they are truly scary.
Even, I don't know if there was the choice of words used in the narrative of the book, since I think that I'd some "technical" difficulties to visualize some of those scenes, if I wouldn't have previous notion of how they supposed to look like, thanks to the film.
PLAYING DEVIL'S ADVOCATE
So, I am still glad of having read the original novel, since not matter the film adaptation covered the most important elements of the general storyline;...
...the novel indeed gives you enlighting info about the background of the characters, even "new" characters that didn't appear on the movie version, and deeper development of many of the scenes.
On the film, you never have doubt that there is a demon inside of Regan,...
...but in the novel, there are plausible scenarios causing suspicions on other characters, with the chance of a more rational explanation.
So, not so ironically, in the same way that you have faith to believe in God, well, the story requires of you to have "faith" to believe in the existence of The Devil.
That, it's something so curious about many priests in Catholic Church, that I understand that there must be an investigation to discard a simpler explanation to some situations, but it seems that if you say that you're possessed by The Devil or to the contrary, you were witness of the word of God, in any case, the priests will see you as a perfect nut job to send to some psychiatric asylum.
So, while the priests are supposed to believe in God, it's like they don't want to believe in the existence of The Devil, that's it's quite odd, since they are both sides of the same religious coin.
Also, some elements in the novel, that you may perceive as "random" in the film version, even not clarify enough for really understanding why they are in the story, those elements are well developed on the novel and even making ties to the demon inside Regan that you may didn't think about before.
Moreover, some reactions and conducts of the characters, knowing key info about their pasts, you can rationalize better why they are reacting in such ways.
Even some conversations, they are the same in terms of dialogue, but the mood of them are perceived in a different way in the book, giving some new angles to the dynamics between characters.
SPEAKING OF THE DEVIL
That's exactly what I expect when I decide to read a book (original novel or novelization) when I already watched the film adaptation.
Since while I invest only two hours to watch the movie, I can invest like a week (or more) to read a novel. So, if I read just the exact story on the book, I think that it would kinda pointless, but if I got enough additional info,...
...certainly then, it was well invested time.
I think that the most effective element on the construction of the story is that you get a lot of arguments and plausible explanations of what it's going on, so in some reverse psychology gimmick, you get to believe more and more that Regan is indeed possessed by a demon.
While in some other novels where they approach the paranormal angle directly, the reader tends to accept it without a doubt.
Maybe you don't believe in The Devil or in God even, but don't worry,...
...since you also can say that you don't believe in Jupiter (the planet, not the Roman god) and that doesn't make that that planet isn't out there.
Many people are atheists until they have to face a demon by themselves.
And it's not like that I am saying that you have to believe in the Christian God, since while I am Catholic, my wish is only that all people believe in some higher power, that you may name whatever you prefer, but believe, in something higher than us.
Since some others may call as unrealistic, to believe in gods or higher powers,...
...for me, not believing in some higher power, I'd call it as sad.
Believe in God. Beware of The Devil. Both are real, not matter if you believe in them or not.
Getting back to the book, I recommend the novel for any fan of the film and wishing to get a deeper developement on the story.
P.S. (Updated Jan, 13th, 2017)
I just knew that William Peter Blatty passed away. I'm glad that I was able to read his most iconic work way before he would die.