Finest example of a very small genre.

Rating: 3/10 (11 October 2008)

...and that genre is "bland eschatology".
The Sixth Sense actually caught me somewhat off-guard, but that's the last time M. Night did so. Signs and the "swing away" thing was somewhat impossible to completely predict, but that just made it harder to buy into, and therefore cost it most of its dramatic effect.
I hadn't heard anything *at all* about The Happening before I gave it a watch on pay-per-view and I have to say this one didn't deliver any kind of twist. I knew what was going to cause whatever bad thing that was going to (sigh) happen the instant the first scene began. When it quickly became apparent it was causing people to arbitrarily act odd and then kill themselves in all sorts of ways, I laughed.
Why? It's not that I'd find such a device in a movie necessarily laughable, it's that the vapid characters and largely unengaging acting made it quickly apparent that the movie was akin to a disaster flick where the disaster itself carries the movie and doesn't have to heavily rely on the individual characters to complete itself.
The problem is, the film doesn't succeed. The causal factor for "The Happening" is implausible, even for someone who doesn't know a monochot from a dichot or a pistil from a stamen. That the film spends the lion's share of itself depicting all the different ways people choose to commit suicide just develops it into a higher-budget "Faces of Death" with worse acting.
A properly written story would have involved people just arbitrarily dropping dead...or, if you wanted something more fitting (and suitably gory), arbitrarily collapsing and writhing around while spontaneously and instantly decomposing into fertilizer. Of course, this would have meant the entire film would require better acting and much better characterization.
TLDR version: Thinly veiled environmentalist admonishment that is poorly written and unbelievably hokey with extremely sub-par acting. Barely worth a rental.