Prometheus doesn't, in any way provide a narrative that directly leads to what happens in ALIEN or the subsequent films. What it does is provide additional context to the back-story and mythology of the ALIEN universe, explaining how profound 'the weapon' (the black goo) is. It also ties the very origin of humanity to this goo and may hint at our true creators.
Thus, Prometheus isn't giving us a direct line of continuity into the ALIEN Series, it's giving us the blueprint to how this universe works.
**CAUTION: SPOILERS AHEAD**
Ultimately it tells us:
- The weapon is at the very least 2000 years old. - When combined with human DNA it causes mutation either in the host, or in the host's offspring, that usually turns against the host. - By mixing the goo with human or humanoid DNA (in the case of The Engineers) the result is something that looks like our 'Aliens'. Thus we can assume this is also how the Aliens on LV- 426 evolved. - We learn that 'The Engineers' seem to want to destroy life on earth using this weapon. Yet one of them seemed to go out of his way to create life on Earth using the same (or similar) stuff. - We learn that for 'the weapon' DNA to create sentiment creatures (versus only taking over the host), the host has to sexually transmit it to another host. This is why Holloway is consumed, but Shaw is impregnated. - We then learn that this impregnation process is rapidly sped up (versus normal human gestation). This tells us a great deal about what to expect in the later series. - While the androids in this universe are somewhat cold and calculating, they are far from 'soul-less'. - LV-223 is where this story takes place. LV-426 is where ALIEN takes place. Thus, barring events that we've yet to be shown on screen, absolutely nothing witnessed in this film shows up in ALIEN or its sequels.
We also learn some other interesting things:
- Weyland lived a lot longer than anyone was aware of previously and actually traveled to 'meet his maker'. - We learn Weyland had a daughter. - It's implied that much of life on earth is still very much an accident. Though the humanoid Engineer apparently seeds the planet on purpose, because he himself dies in the process, there was no 'guiding hand' that lead humanity to where it is up the the point in the movie. - It's inferred that the events of this movie take place in the same star-system (but not the same planet) as the events in ALIEN. - We learn that The Engineers have traveled the stars for far longer than human civilization has existed. - We learn either The Engineers either left early warnings or early invitations about how and where to find them (the humanoid figure pointing to a four planet system).
Contrary to all the griping on this (and other threads) Prometheus is a very well thought-out story. It deftly serves as a prequel without having to maintain (or counter) any established continuity. It aims to be prolific in it's goals, while being subtle in how it crafts itself around ALIEN-lore. That said, do I think it made for a good movie?
Good? yes. Great? no. I rated this movie a 6 out of 10. Only slightly better than average. Though a great story is crafted here, it suffers from some really odd plot gaffes (let's not call them holes) and poor characterization. Examples:
- A geologist who gets lost in a cave that he is the one responsible for mapping. - Another scientist who decides the strange creatures following him must be friendlies. - We have a rather annoying moment where two scientists can't figure out that, if an object is falling on you vertically, running horizontal or diagonally would be the advised choice. - A catatonic Engineer is awakened after 2000 years, yet rather than being dumbfounded or in awe that humans (and an android) have traveled light years to find him - he simply tries to destroy them all at first site. - Much like with the Star Wars Prequel/Sequels the technology on display in the (later filmed) earlier films is unnecessarily more advanced than in following films with no explanation.
Great story. Great addition to the franchise. So-so film.