An early draft of the script for Prometheus has been published by a fan site this week. Titled Alien: Engineers, it reveals alien creatures and plot points never seen in the finished film.
The movie faced criticism surrounding the vague nature of the film leading to some rather significant plot holes, partly down to Lost creator Damon Lindelof's contribution. This early script represents the original storyline penned by Jon Spaihts, and puts across (more or less) a direct prequel to Alien.
New plot twists involving Facehuggers, an explanation into why Milburn and Fifield (the two who are killed first by the alien snake and black goo) are such idiotic scientists, a trip to Weyland base on Mars, more horrific scenes akin to the caesarean, and a name change from Shaw to Watts. Many of the holes are filled and, quite frankly, this could've made for a better film.
Spaihts himself confirmed the authenticity of the script on Twitter, providing more details. It's one of five "official" drafts made over the time of writing Prometheus, and key scenes were cut due to budget constraints.
The Prometheus that could've been. It's a fantastic read.
Source: Prometheus Forum