'The Omen' scared the bejesus out of me as a kid. Watching it again all these years later much of its impact has worn off, and yes, it has dated quite badly, but it's still a wonderfully entertaining movie, probably second only to Polanski's 'Rosemary's Baby' in the Satanic/apocalyptic genre. It definitely wipes the floor with recent pretenders like 'Lost Souls' and 'End Of Days'.
One of the reasons it still works is that the actors take the (sometimes silly) material so seriously. And when you have actors of the calibre of Gregory Peck and David Warner it certainly helps. Peck is utterly convincing as the Ambassador who doesn't want to believe the shocking facts staring him in the face, and Warner, who often found himself in second rate b-grade rubbish, obviously relished his role as the inquisitive reporter who helps convince Peck that things are not as normal as they seem. Along with Peckinpah's 'Cross Of Iron', one of his best roles. Lee Remick is strong as Damien's worried mother, Billie Whitelaw chilling as the mysterious governess, and Patrick Troughton ('Dr Who' #2) is very good as a dying priest who knows the truth about the Thorn's son.
Forget the sequels, 'The Omen' is classic Satanic schlock, and still has more than a few scares left in it. Essential viewing for fans of 70s horror.