Ridley's design criteria for the engineers' world

(leading from : The Space Jockeys renamed The Engineers)

engineer in Prometheus trailer

In attempting to understand PROMETHEUS’s connection to ALIEN, for which H.R. Giger designed the reptilian, skeletal and iconic look of the Xenomorph alien, Max says he had a clear direction from Scott. “Ridley said, "I don’t want it to be too Giger-y, but I don’t want to give it all up either."  The art department looked at design work Giger had achieved for the first ALIEN film, in the form of archival files retrieved from the Motion Picture Academy Library and from the personal collections of those who’d worked on the first film. Ridley also screened some of the genre’s most definitive works. “He had accumulated a lot of research based on the original movie and the whole series,” remembers Max. “We watched all those movies. Ridley had us screen ALIEN and BLADE RUNNER, and a lot of movies with ‘STAR’ in the title. There’s three of them. I’ll let you figure out which ones!”
Watching the reference material was as much about discovering what not to do. “We didn’t want to be like any one of those,” Max explains. “We wanted to be new and fresh because, I hate to admit it, otherwise it really dates us. We decided to make it less biological, in terms of the styling of the alien planet, and more mechanical.”  

Max summarises the key challenge of envisioning the alien environment: “The people who inhabit this planet, called the Engineers, and their technology, is beyond anything we’re able to know or understand, but it has to be visually interesting. That’s, I think, the hardest challenge, too, because we have to compete with the most iconic science fiction creature ever. Trying to come up with something that’s going to rival that is the real trick.” (Source: spotlightreport.net)