It's common now to see studios spending big money on genre pictures and as a rule, horror and science fiction films don't look like ratty B-movies anymore (if a genre film is made on the cheap, like Paranormal Activity, it's the stuff that headlines are made out of). But in 1979, it was still relatively rare to see a science fiction or horror film treated like an A-movie. One of the criticisms leveled at Alien, in fact, was that some found it obscene that so much money had been lavished on such a flimsy story (if these people only knew what the future held for cinema!). But Scott was a stylist who initially honed his craft in commercial work (the kind of professional background that came to be common among directors) and the look that he gave Alien was indispensable to the film's success.
The trailers for Alien were every bit as strikingly designed as the film itself and as opposed to the recent sci-fi/horror film Pandorum - which while being a more than decent movie, could not have had a murkier, more unappealing ad campaign - whoever was in charge of getting the word out on Alien back in the day hit a bullseye. With only giving the sparest idea of the story, and without including any lines of dialogue (or a good glimpse of the alien itself), the teasers and trailers for Alien conveyed the most important fact about the movie - that it was going to terrify you. "In Space, No One Can Hear You Scream" still holds the title as Best Tagline Ever, topping even The Texas Chainsaw Massacre's infamous "Who Will Survive And What Will Be Left Of Them?"
Watching these trailers again, it makes me wish that someone today would be able to take the kind of resources that Scott had to work with and apply them towards making a movie that wants nothing more than to be mercilessly frightening. Nowadays when a horror film has a big budget, it usually has to be a PG-13 hybrid of action and horror but Alien remains the rare instance where a big budget film put everything it had towards scaring an audience senseless.
For a better quality version of the above trailer, click here. And here's a TV spot that carried over the memorable 'egg' imagery from the trailers.