The scariest sequence I can remember is in Night of the Living Dead. The cemetery-visiting heroine, Barbara, is chased back to her car by a lurching zombie with white hair and dazed eyes. She locks herself in only to discover her brother has taken the keys. The zombie reaches down, finds a rock, and begins to bash it strengthlessly against the car window. The first time I saw this (and twice after), the scene reduced me to jelly.
Of Fox's two summer creepshows, give the edge to The Happening, partly because M. Night Shyamalan really understands fear, partly because this time he's completely let himself go (hence the R rating), and partly because after Lady in the Water he had something to prove. And, happily, Happening plays as a relatively small movie. The new X-Files movie, on the other hand, looks big...but horror is not spectacle, and never will be. Horror is an unknown actress, perhaps the girl next door, cowering in a cabin with a knife in her hands we know she'll never be able to use. Horror is the scene in The Strangers where Liv Tyler tries to hide beneath the bed...and discovers she can't fit there.
One more problem: Big movies demand big explanations, which are usually tiresome, and big backstories, which are usually cumbersome. If a studio is going to spend $80 or $100 million in hopes of making $300 or $400 million more, they feel a need to shove WHAT IT ALL MEANS down the audience's throat. Is there a serial killer? Then his mommy didn't love him (insert flashback). A monster from outer space? Its planet exploded, of course (and the poor misunderstood thing probably needs a juicy Earth woman to make sexy with). But nightmares exist outside of logic, and there's little fun to be had in explanations; they're antithetical to the poetry of fear.
That's why I can't imagine that anything in X-Files will match Liv Tyler's exchange with one of the masked home invaders in one particularly terrifying scene of The Strangers.
''Why are you doing this to us?'' she whispers.
To which the woman in the doll-face mask responds, in a dead and affectless voice: ''Because you were home.''
In the end, that's all the explanation a good horror film needs.