In all the three films directed by M. Night Shyamalan that I've seen, the same plot device has been used to achieve decent results. That plot device is clearly illustrated in Shyamalan's latest effort, Signs: nothing that happens in a film happens by coincidence.
In The Sixth Sense, we had the protagonist go through life's motions only to discover a revelation involving what he thought was his life. In Unbreakable, we had a villain whose character was created by his own actions to uncover his polar opposite. In Signs, we have a person who has stopped believing in a god (not really) but finds out that, you guessed it, everything happens for a reason.
That person is Graham Hess (Mel Gibson), who has just lost his wife and his faith in a god. He's actually angry at god more than anything else, and like his two children, says things that he doesn't really mean. When the aliens invade (the crop circles are used as navigational aids), it looks as though the world is about to end. The question is "why?"
Signs is really an allegorical alien invasion story, but with the Shyamalan plot device behind it. Thus it's not really about the aliens, but the "coincidences" (signs) that all seem to happen for a reason. I don't quite understand how people could not be satisfied with the ending, because like with the two other films, everything is tied up neatly. The closure is more complex and less telegraphable than the one in The Sixth Sense, but not the one in Unbreakable (which is my favourite Shyamalan film).
The Sixth Sense, M. Night Shyamalan's first directorial effort, was a highly overrated film: the unexpected closure was based on a preposterous assumption (The Others handled the same plot device a lot better). Unbreakable represented a significant improvement, making the setup for the final structure much more richer and more consistent. Signs' closure is rapid, but like the other two films, repeated viewings should probably show more signs that people have missed.
As with his previous films, the pacing was slow enough to get me yawning a few times but it does appear that Shymalan has a good feel for when it's too much. There are some suspenseful and scary moments, with a lot of humour to relieve the tension. All the actors give solid performances, and the score by James Newton Howard is excellent. There's a lot of humour in the film. It's clear the director is paying homage to several movies given the mimicry of the scenes (Birds, War of the Worlds, Close Encounters of the Third Kind, etc.).
During the film, the claim is made that there are two types of people in the world. Those who believe in determinism, and those who believe that life is pure chance (Einstein was wrong). What Shyamalan doesn't realise is that the latter group cannot have a concept of an absolute good or bad. As someone who does believe events in life are completely dictated by chance, all events that happen are good or bad depending on your perspective, akin to viewing whether a glass is half-full or half-empty. This viewpoint results in a full circle that is colinear with the first one. This is why the distinction made (like most dualistic forms of reasoning) is a false dichotomy.
It's not clear whether Shyamalan believes what he writes about. Either he believes the pseudoreligious tripe that people seem to derive from his films, or he's one of the great manipulators of a society where people look for spirituality and a sense of purpose (give me Sartre any day). Either way, every story he narrates requires careful well thought out planning, and Signs is definitely worth watching on the big screen to see how everything fits together.