I thought the riffing was pretty good on this one. It truly was an awful movie. I tend to divide movies into two classes, the kind that are awful in retrospect and the kind that you know are awful as you're watching them. Of the ones riffed here that I've seen, the ones that fall squarely into "awful when you're watching" are Transformers, Battlefield Earth, Crystal Skullfuck, Matrix sequels and the Star Wars prequels.
M. Night movies are more frustrating because you don't really have an appreciation for how awful they are until afterward. Sixth Sense was the only good movie he's ever made. The rest of them I've seen, you keep watching because you think something good might be happening until you get to the end and, having experienced the entirety, realize its entirely awful, even the parts you first mistook as entertaining. Its kind of like drinking heavily all night and not quite realizing until the chunks are flying that however good a time you were having, its not a good time anymore.
The thing that was so deceptive with the advertising of the Happening is that I thought the whole bit was about scary floating bodies. We saw legs dangling in the trailer, not knowing they were suicided lawn workers hanging from trees. We saw the construction worker bodies falling from the building. It looked a whole lot cooler and mysterious than plant nerve gas. And I'll admit that I'm a total sucker for disaster horror movies like this, I was totally sold on the premise alone. But wow, this ended up being exactly like the awful B-movies from the MST3K days.
My favorite part is the low-rent villain, a big fan off-screen blowing at trees. Shit, I'm going to write my own spec script called "The Invisible Monster Nobody Can See Who Kills You Not With Expensive Gore Shots But By Having You Writhe On The Ground Like You Were Dosed With Nerve Gas Which Can Be Accomplished With Crappy Acting." So we'll just have the camera track nothing across the room while cutting to reaction shots of scared actors, dub in some pig squealing that's been reversed and reverbed so it'll sound demonic. The actors will scream and fall and play dead. It'll be the cheapest movie ever.
Random rant on Signs, what I learned from the movie: if I ever get my own flying saucer, it would make sense for me to get my friends together and go invade a planet where hydrochloric acid rains from the sky, where oceans of the stuff lay between the continents, where the very creatures I seek to enslave are 70% acid by mass .And then I'll invade this planet naked. Makes about as much sense as these aliens invading a planet filled with the stuff that makes them go all Wicked Witch of the West.