Prometheus is neither as good or as bad as you think or have heard it is.

The film begins promisingly, showcasing impressive 3D and awe-inspiring visuals as a team of anthropologists and scientists set out to discover the origin of human life. The events in the first hour and a half are as thrilling and chilling as any memorable entry in the sci-fi and horror genres. And then, almost as if rewritten at the last moment, the narrative morphs and changes, becoming as truly unsatisfying a third act as any in recent memory. Prometheus suffers from what I am calling my Will Smith Theory of Devolution — named aptly for the actor frequently featured in films (I Am Legend, Hancock, Men in Black³) that suffer from this affliction — wherein something occurs at some point in a well-crafted narrative that so completely alters our characters such that they do things that are confusing to an audience. If you think of the part, you will hate the whole. If you recall the whole, you may not entirely hate the part.

But when Prometheus works, it works wonders. Only tangentially riffing on his Alien (1979), director Ridley Scott utilizes the finest visual effects and a superstar cast to the peek of their powers. When we come upon The Prometheus, the human vessel headed for a distant moon of a planet in a galaxy referred to only in prehistoric paintings found on several of remote cave walls around our Earth, the crew is being watched over in hyper-sleep by David (Michael Fassbender), an android whose loyalty to utility is only trumped by his curiosity for absolute truth. As the approach the planet, the robot wakes the humans, who vomit, eat, and suit up for the impending planet.

As they descend on the planet, the human crew of The Prometheus quickly stumble upon a massive pyramid, where anthropologists Elizabeth Shaw (Noomi Rapace) and Charlie Holloway (Logan Marshall-Green) determine could be the birthplace of humanity. Corporate bigwig Meredith Vickers (Charlize Theron) is more skeptical. Janek (Idris Elba), the ship’s captain, is more wary. These are actors at the top of their game, but are all out-shined by Fassbender, whose ever-calculated but not calculating David haunts both the ship and the pyramid as if a curious ghost. The android, as written by Damon Lindelof and Jon Spaihts, is perhaps the greatest non-villain ever committed to screen, making moves in a game to which he knows none of the rules but seems certain of the outcome.

As the greatest sci-fi stories have promised, the truest and most visceral horrors await at the edge of space, and the film’s finest moments are in the catacombs of the pyramid, where the sights and sounds at first delight, then horrify, but always creep. Prometheus features a variety of freakish creations, the greatest of which are Gigerian monsters with acidic blood leeching onto their victims and infecting them with something parasitic. Is it a surprise to announce the film features an graphic, on-camera alien abortion? Any franchise so utterly based on alien impregnation had to get here eventually.

But as I’ve already said, while 75% of this movie works so completely well, the remaining quarter of the movie’s elements range from confusing to annoying to downright stupid. Much of this muchness is due to the presence of Peter Weyland (Guy Pearce), the decrepit corporate financier of the mission. We see him early, and we are not surprised when we see him again — always bizarrely written and ever out-of-place. Perhaps this is an inherent result of having a 44 year old actor playing a very, very old man seemingly without reason. While Pearce’s performance is fine enough, his character throws off the motivations of everyone else in the story, and muddles everything up into the film’s frustrating conclusion.

As far as Prometheus being an effective prequel to Alien, and by association, Aliens (1986), Predator (1987), Predator 2 (1990), Alien³ (1992), Alien Resurrection, AVP: Alien vs. Predator (2004), Alien vs. Predator: Requiem (2007), and Predators (2010)? Does it stay in-keeping with all the mythos? I really can’t say. From my memory, I’m pretty sure there are some continuity errors. But I think Prometheus is beyond its prequel trappings, and nearly every element (short of the vaginal design of the creatures) grifted from the original Alien actually plays to the film’s detriment. Everything that sucks about that third act? That’s all franchise crap.