"Signs" is M. Night Shyamalan's version of the old alien invasion scenario. Although the advertising for the movie holds out the promise of an X-Files sort of mystery involving crop circles, the movie itself wastes no time making it clear that aliens have come to Earth and are preparing an invasion force. It's all downhill from there, as Shyamalan attempts to use his trademark blend of mysticism and family values in a genre that simply doesn't mesh well with these themes.
All of the motifs Shyamalan used so well in "The Sixth Sense" and "Unbreakable" can be seen in "Signs" as well. The family recovering from traumatic events, the broken father figure who has to confront his loss of faith, the precocious child who instinctively knows the answers to all the mysteries, and even a helpful ghost of sorts. These things had their place in the previous movies - superhero stories and ghost stories are all, to an extent, about faith and destiny and traditional morality. By using these themes, and emphasizing the human aspect of his stories rather than the grand conflict, Shyamalan managed to put a human face on stories more traditionally associated with the mysterious and the numinous. "The Sixth Sense" showed us one of the most believable ghosts in the history of the genre; "Unbreakable" did not quite make superheroes believable, but presented us, through an emphasis on realistically flawed characters and family dynamics, with a quietly magnificent origin story. Both movies managed to almost completely dispense with the dazzling special effect shots and intense action of their genres, and still work as unusually taut thrillers.
The problem is that these things don't work with the science fiction conflict of "Signs". In fact, they make the conflict completely meaningless. The aliens, in the final analysis, are nothing but an obstacle in the father's search for his lost faith. The movie isn't really about Mel Gibson fighting the alien invasion singlehandedly, it's about Mel Gibson putting his priest's uniform back on and getting a new dog.
Since most of you probably won't take my word for it and will want to go see the movie anyway, I will refrain from doing my usual detailed listing of plot holes. Two more things have to be said, though - Mel Gibson gives us some of his worst acting ever, and since the aliens are really nothing but a huge plot device, Shyamalan didn't bother to put any work into making them logical. Their biology is incredibly, horribly wrong, and is a huge slap in the face to all science fiction fans. Feel free to /msg me if you disagree, upon which I will give you a list of books to read. Just some basic biology and Science Fiction 101.
If you want to see this sort of thing done right, check out the following:
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