The Omen was nothing but an Exorcist rip-off.
If you watch "The version you've never seen" with the commentary, you'll get a better understanding of the film. I loved how Friedkin explained how he always potrayed Father Karras (Merrin) climbing up stairs as a metaphor for going up to heaven only to have him crash down to hell (lost his faith in God) when he's mother died (guilt) or how mortal people are when an innocent 12 year-old girl can be possessed. There's alot of substance to this movie. I cant' say the same for " The Omen" which had an Armageddon like theme The Exorcist is about regaining your faith and overcoming obstacles.
The Omen copied the child, dog, housemaids, politicians, and so on seen on the Exorcist. The Exorcist also had better chilling scenes like the crucifix masterbation and the obscene language "motherfudger" and "lick me". I couldn't sleep after that "Spider" scene.
The Devil and the demons were fun to follow in the Exorcist.