I'll play the contrarian: I really enjoyed the film. The higher meanings and the semi-surprise ending worked for me. It's a spiritualized Twilght Zone episode.
James Newton Howard is so attentive to the plot and underlying emotions of each scene that the music becomes indispensable. Other reviews have rightly mentioned the Bernard Herrmann minimalism. The three-note motif is a similar tactic to the five-note signature of "Close Encounters." Howard's intent with the opening theme was to create what he called "[...]a context of expectations." The music telegraphs that at SOME point, something big is going to happen to go along with it.
Normally, the music will change to mark a shift in location (city, country, planet). Since nearly all of this movie occurs within 20 acres, the repetition and thematic simplicity reinforce the claustrophobic atmosphere of the film. Still, this presents exactly the same problem as with John Williams' score for "Minority Report." Parts of the score become TOO sedate when removed from the film.
The furthest Mel Gibson's character gets from the confines of the farm is in flashback dreams of his wife. In turn, that memory keeps him cooped up under his roof, trying to hide from God. Howard uses warm strings to signify the issue of faith gently working its way back into the Hess household. Changing which instrument does the three-note trickle greatly varies its mood and effect.
The subdued nature of the score also gives the crescendos more punch ("Into The Basement," "Asthma Attack," and "The Hand of Fate - Part I") There's a thread of heartland Americana in the gentler parts of the score, particularly in "The Hand of Fate - Part II."
The music and the film are a great partnership. On its own, the soundtrack is worth getting for the energy of the first track, and of the last three.