Does the director strictly follow the book or not? That is an endless question...but it does not address the movie on its own terms. I imagine precious few films actually follow every aspect of a novel, yet they can be quite successful.
As my title suggests, the closest parallel to this movie are the film versions of "Crime and Punishment." In Dostoevsky's book, Raskolnikov deceives his own conscience by murdering a mean-spirited moneylender. It sounds so reasonable on the surface. Alas, the evil inevitably follows him like a shadow. Essential to the book and the films are the cat and mouse interrogations by the Police Inspector Porfiry of Raskolnikov where the officer hints why so many criminals ultimately confess - to calm their own soul.
Now to "The Quiet American." Because other reviews discuss the plot, I include some spoilers...so if this disturbs you, stop HERE. In his sexual rivalry with a young idealist American who falls in love with his beautiful Vietnamese mistress, Thomas Fowler let's himself be manipulated to let others murder the American for political reasons. Fowler himself has just selfish not political reasons to set his rival up.
Possibly the best section of the movie is the ending - the clever, piercing interrogations by Police Inspector Vigot of Thomas Fowler about the crime. Fowler believes his intelligence as well as his non-participation in the actual physical parts of the crime can save him from conviction.
Does Fowler have a way out...I don't mean a way to deflect blame to others... but a way out for his own soul? A way out to explain his conduct to others, including his lover, or himself? A way out to God? This movie answers that question in a devastating way. I can't say enough good things about Michael Redgrave's performance as Thomas Fowler, a world-weary, intellectual reporter unable to comprehend or control his dark, powerful passions. [I can't think of another performance by this British actor that is more perfect than the one he offers in this movie].
As regards comparison to the newer version of the movie, made in 2002, no doubt about it...that later film is extremely well made. Nevertheless, this 1958 picture touched my sentiments in a deeper place. Subjectively, then, I prefer this version.