As much as many people agree that the series eventually underwent a spectacular self destruct sequence in later sequels, several of the critical flaws complained about in the sequels were first brought aboard the ship in the better received earlier films.
- Later films in the series, such as Prometheus and Alien: Covenant, have been torn apart by viewers due to the characters' firm grasp of the Idiot Ball, leading to many cringeworthy moments (the run from the crashing Derelict ship in the former and Oram's death via Facehugger in the latter come to mind). However, this was also a part of the acclaimed first two entries, with the crew of the Nostromo in Alien and the Colonial Marines in Aliens also making boneheaded decisions multiple times throughout the films, leading to many of the deaths that happened in them. But it was excused in those movies because the Nostromo members were space truckers dealing with a threat that was well out of their depth (and add on the fact that their science officer is secretly a company android programmed to bring back any valuable specimens, even if it's to the detriment of the other crew members), and the Marines likewise were an allegory for American soldiers in the Vietnam War, their overconfidence leading to their deaths. Furthermore, both parties acted logical in the sense of making choices a person would realistically do. To start, Ripley in the first film chose to not let the team back on until they followed quarantine protocol, only for Ash (the aforementioned android science officer) to ignore her decision (and even provide a reasonable explanation later on as to why he did so). And in the second film, the Colonial Marines still used what would be perfectly smart tactics and strategies in most other combat situations, but said strategies and tactics were simply not meant for enemies like the Aliens. Prometheus and Covenant however had crews made up of top-tier scientists and colonists respectively, all of whom are supposed to be intelligent and be better prepared for potential danger compared to the crew of the Nostromo or Marines, thus it was much harder to look past, as seeing these supposed "professionals" die due to idiotic moments that they realistically should have been smart enough not to engage in ultimately stretched Willing Suspension of Disbelief too far.
- In addition, the later films have been criticized due to giving both the Space Jockey and the Xenomorphs rather lame backstories and history, with many saying that they cheapened the overall mythology. This can be traced all the way back to the second film, which did away with portraying the Xenomorph as a One-Man Army capable of destroying an entire crew alone, along with being barely visible and with a rather disturbing method of birth, to an entire species of disposable grunts answering to a Queen who essentially creates the hive. That right there demystified much of the aura surrounding the Xenomorph of the first film, which even some feeling that it ruined the whole point of the original monster. That said, the Xenomorphs were still shown to be fearsome opponents, easily taking out all but one of the Marines, and the Queen itself remained a mysterious entity. Viewers were less forgiving when Prometheus revealed that the Space Jockey was merely a humanoid alien in a suit and that the Xenomorphs were revealed in Alien: Covenant to be merely the creation of the android David, as these got rid of any mystique that they had, turning them into stock horror villains to many. Their easy demises in these two films certainly did not help.
- Many fans consider Aliens the best film in the entire franchise, and it's even been called one of the best movie sequels in the entire history of film (alongside The Empire Strikes Back and The Godfather Part II). It was also the first film in the series that was more about Ellen Ripley than about the titular aliens, which played a major role in the series' decline. It's easy to forget this today, but the original Alien was an ensemble film that didn't really have a clear protagonist until the final act; Ripley was originally just "Warrant Officer Ripley", a humble mid-level crewman on the Nostromo who unexpectedly managed to outlive her crewmates with nothing but courage, cleverness, and plain old luck. Her survival was all the more impressive because she wasn't advertised as the main character, so it actually seemed believable that she could die at any moment.
Then in Aliens, Ripley Took a Level in Badass as she settled into the protagonist role from the beginning, becoming a true Action Girl who could make the audience cheer. There was certainly nothing wrong with that change; Sigourney Weaver's performance as a gun-toting Mama Bear is legendary for a reason, and it's still considered a defining moment for women in cinema. But it made Ripley quite a bit less relatable, turning her into more of an Action Hero than an Audience Surrogate. It also robbed the movies of a lot of their tension, since nobody seriously believed that the aliens would kill the protagonist. However, Ripley starts off the film suffering mental trauma from her experiences, and doesn't become a badass right away, but grows into it as the story develops, so she starts off pretty relatable still. Alien³ took that trend further when it killed off Ripley's Love Interest Hicks and her surrogate child Newt, and brought her back into conflict with the Xenomorphs through a blatant Diabolus ex Machina, turning her into a stoic Action Survivor who didn't seem to have much of a life outside of battling aliens (which the film Lampshades) and was destined to do so all her life. But even then, the film's Central Theme was all about accepting one's mortality and making amends before death, which is viscerally intuitive to most audiences and thus helped to preserve her humanity and viewers' investment in her inner-turmoil. Then Alien: Resurrection just took the trend to its logical conclusion when it brought Ripley back from the dead merely to justify her continued presence in the movie, then turned her into a bona fide superhuman with alien DNA. - Monster Threat Expiration was a commonly cited problem in the Alien vs. Predator films and in Alien: Covenant, where both the Predators and the human characters have no problem holding their own against the xenomorphs. This problem dates all the way back to Aliens. The original Alien only had one xenomorph attacking the crew of the Nostromo, and on its own, it was an extremely dangerous threat, but in Aliens, the Xenomorphs were beyond counting, yet the protagonists slaughtered them relentlessly. The difference was that the human characters were far more powerful in-universe — instead of the lightly-armed crew of a civilian freighter who couldn't make use of powerful weapons lest they destroy the ship (between the xenomorph's acid blood and the fact that the Nostromo wasn't built to have guns and explosives going off inside), the xenomorphs were up against Space Marines (and Ripley, who knew their weaknesses after facing one before) on the surface of a planet who were free to use far more powerful weaponry up to and including nuking the entire site from orbit — and even then, attrition, carelessness, and overconfidence eventually destroyed The Squad. The AvP films and Covenant, on the other hand, turned the xenomorphs into generic alien baddies for the main characters (who, on the human side, were mostly scientists, colonists, and other civilians rather than soldiers) to fight, and can be often taken down with a single headshot stripping them of much of their menace.
- In relation to Monster Threat Expiration, Alien films have also increasingly violated the principle of Nothing Is Scarier as the films have progressed. In addition to keeping the monster hidden for much of the film (both for Rule of Scary and to prevent the audience from realizing how fake the rubber suit looked), the first movie kept the monster's abilities and traits a secret until it was it was the most scary. This reinforced the premise that mankind was facing a truly unknown and unknowable entity that could kill us in ways we couldn't even imagine. This is further shown in deleted scenes and unused drafts in the original film, where new powers the alien possessed were still being discovered, such as its ability to horrifically morph living or dead people into new eggs or its ability to bite off someone's head and then mimic their voice and use intelligent language. In Aliens, the abilities of the xenomorphs were nailed down: they're animals, albeit very smart animals, and the limits of their abilities aren't anything that wasn't seen in the first film. This was excusable in that movie because the balls-to-the-wall action and suspense were still entertaining, and the existence of the Alien Queen gave one final surprise to the whole affair. But in the following films, we had seen it all before. In order to keep things interesting, the writers had to do things like take away the heroes' weapons in 3, have the aliens fight Predators, and hybridize the aliens with other creatures like dogs, Predators, and Ripley herself. At that point, it was clear that a xenomorph on its own could no longer cut it as an antagonist.
- Some supporters of the first Alien vs Predator movie tend to defend its cast of humans from the accusation of being "not deep" or "uninteresting" by citing that the supporting characters of the original Alien, Aliens and Predator weren't given a lot of fleshing out either. This ignores that most of those 'OG undeveloped characters' were played by strong actors directed by three excellent directors during their prime and thus could inject a lot of humanity and charisma into their roles to the point it didn't matter if there weren't exceptionally deep on paper, and even then they were still given a lot of memorable lines that have become iconic. AVP on the other hand offers a generic cast of Red Shirts who use very clichéd Slasher Movie victim tropes such as a Fatal Family Photo (something none of the original films relied on in order to make audiences care for the characters), under the serviceable-at-best direction of Paul W.S. Anderson. There's a difference between being "not very deep" and being "uncharismatic and forgettable" when it comes to the art of Developing Doomed Characters.
- A minor criticism of Prometheus and Covenant is the use of on-the-nose Religious and Mythological Theme Naming which sounds pretentious and obvious for the ships, (the ship named Prometheus ends up stealing technology from godlike aliens? What a coincidence!) But, the ship in the original Alien movie is called Nostromo, a reference to the 1904 novel of that name, whose plot has many parallels with the movie. It wasn't a big deal then, because Nostromo makes sense as a ship's name (if you assume Space Is an Ocean) and is neither overly grandiose nor a central part of the movie's identity.
- On a related note, the usage of religious themes and imagery in general was already present in the franchise as far back as the original Alien film. But while the original film kept such elements reasonably subtle (in the form of a Genius Bonus involving the ship's name, a minor aesthetic detail in the form of the cross-like shape the orifices of the eggs take when they hatch, and a brief joke in which the newly 'born' alien aboard the ship is lightheartedly referred to once as 'Kane's son'), Alien³, Prometheus, and Alien: Covenant made usage of these elements to a much more unsubtle and Anvilicious degree, which resulted in the films drawing strong criticism for trying to make themselves look deeper and more insightful than they actually were.
