David Giler declared in 1979 Brandywine Productions were intent on "immediately making a sequel" to Alien, having the full support of 20th Century Fox President Alan Ladd Jr.. However, that year Ladd left amid Fox's transition to new owners Marc Rich and Marvin Davis, and the new studio management had no interest in the sequel. Giler accused new President Norman Levy of being the one that held back the film's production; Levy would later declare that "It was a movie I wanted to make," but he felt another Alien would prove too costly. In the meantime, Giler and partners Walter Hill and Gordon Carroll sued Fox regarding the disbursement of the Alien profits. By the time the lawsuit was settled in 1983, Fox had new executives that got interested in continuing Alien. Giler pitched the project to one of the executives as a cross between Hill's Southern Comfort and The Magnificent Seven.

Critic Roger Ebert gave the film 3.5 stars out of 4 and called it "painfully and unremittingly intense" and a "superb Example of filmmaking craft." He also stated "when I walked out of the theater, there were knots in my stomach from the film's roller-coaster ride of violence." Walter Goodman of The New York Times said it was a "flaming, flashing, crashing, crackling blow-'em-up show that keeps you popping from your seat despite your better instincts and the basically conventional scare tactics." Time magazine featured the film on the cover of its July 28, 1986, issue, calling it the "summer's scariest movie". Time reviewer Richard Schickel declared the film "a sequel that exceeds its predecessor in the reach of its appeal while giving Weaver new emotional dimensions to explore." The selection of Aliens for a Time cover was attributed to the successful reception of the film, as well as its novel Example of a science-fiction action heroine. Echoing Time's assessment, Dave Kehr of the Chicago Reader called the film "one sequel that surpasses the original." On the negative side, Gene Siskel described Aliens as "one extremely violent, protracted attack on the senses" and that "toward the end, the film resorts to placing a young girl in jeopardy in a pathetic attempt to pander to who knows what audience. Some people have praised the technical excellence of Aliens. Well, the Eiffel Tower is technically impressive, but I wouldn't want to watch it fall apart on people for two hours."

Aliens was first released on VHS in 1987, finishing as the tenth-best-selling title of the year. A "special edition" of Aliens was released on LaserDisc in 1991 and on VHS the following year that restored 17 minutes of deleted footage. These additions include a segment showing Newt's family first encountering the derelict spacecraft on LV-426, Ripley's learning that her daughter died during the years she was in hypersleep, a scene in the operations building in which the marines use sentry guns against the aliens, and several extended dialogue scenes between Ripley and the marines. These scenes had been deleted from the original theatrical release as 20th Century Fox representatives thought the film was showing "too much nothing" and spent an unnecessary amount of time building suspense.

Most of the special edition's footage was first seen when the film made its broadcast television debut on CBS in 1989, but two additional sequences concerning Burke's transmission to the colony about the derelict, and the Jorden family's subsequent discovery of the same, were added to the initial Laserdisc release. According to Cameron, the visual effects for the scene were incomplete, so he went back to the Skotak brothers and had them finish the sequences. All currently available versions of the special edition contain these scenes.

The android character Bishop has been the subject of literary and philosophical analysis as a high-profile fictional android conforming to science fiction author Isaac Asimov's Three Laws of Robotics and as a model of a compliant, potentially self-aware machine. His portrayal has been studied by Writers for the University of Texas Press for its implications relating to how humans deal with the presence of an "Other", as Ripley treats them with fear and suspicion after the android Ash tried to kill her in the original Alien movie, and a form of "hi-tech racism and android apartheid" is present throughout the series. This is seen as part of a larger trend of technophobia in films before the 1990s, with Bishop's role being particularly significant as he doubly proves his worth at the end of the film, thus confounding Ripley's expectations.

A sequel, Alien 3, was released in 1992, with Weaver reprising her role as Ripley and Henriksen as Bishop in the film.

Horner stated that tensions between himself and Cameron were so high during post-production that he assumed they would never work together again. Horner believed that Cameron's film schedules were too short and stressful. The two parted ways until 1997 when Cameron, impressed with Horner's score for Braveheart, asked him to compose the score for Titanic.

Reviews of the film have remained mostly positive over the years. In a 2000 review, film critic James Berardinelli said "When it comes to the logical marriage of action, adventure, and science fiction, few films are as effective or accomplished as Aliens." Austin Chronicle contributor Marjorie Baumgarten labeled the film in 2002 as "a non-stop action fest." In 2016, James Charisma of Playboy ranked the film #6 on a list of 15 Sequels That Are Way Better Than the Originals.

The film is also recognized by American Film Institute in the 2003 list AFI's 100 Years...100 Heroes & Villains: Ellen Ripley as the #8 hero.

Time magazine named Aliens in its Best of '86 list calling it a "technically awesome blend of the horror, sci-fi and service-comedy genres." In 2007, Entertainment Weekly named Aliens as the second-best action movie of all time behind Die Hard. In a Rotten Tomatoes analysis of the top 100 science fiction films, Aliens ranks tenth among the best-reviewed films of the genre. In 2004, Aliens was ranked 35th on Bravo's "100 Scariest Movie Moments" for the scene in which Ripley and Newt are attacked by facehuggers; the original Alien was ranked second for the chestburster scene. IGN ranked it third in its "Top 25 Action Films of All Time", stating that "there won't be an Alien movie as scary—or exciting—as this one made ever again." Empire voted it the 'Greatest Film Sequel Of All Time'.

The film holds a 98% "Certified Fresh" rating on Rotten Tomatoes based on 65 reviews, and an average rating of 9/10. The site's critical consensus reads, "While Alien was a marvel of slow-building, atmospheric tension, Aliens packs a much more visceral punch, and features a typically strong performance from Sigourney Weaver." It also holds a score of 86 out of 100 based on 10 critics on Metacritic, indicating "universal acclaim". Aliens was also featured in Empire Magazine's 500 Greatest films of All Time poll at #30 in 2008, in Empire's 301 Greatest Films of All Time poll at #19 in 2014 and in Empire's recent 100 Greatest films of All Time poll at #15.

Early concept art was created by Syd Mead, who had previously worked on Blade Runner, 2010, and Tron. One of the original designs for the spaceship Sulaco was spherical, but it was redesigned as the ship would be out of frame due to the film's aspect ratio. Cameron showed Mead his own concept art, and the final result was described as "rocket gun that carries stuff". Concept artists were asked to incorporate subliminal acknowledgments to the Vietnam War, which included designing the dropship as a combination of a F-4 Phantom II and AH-1 Cobra.

In 2013, National Entertainment Collectibles Association (NECA) released the first wave of highly detailed human and alien action figures from the respective film. NECA's Reel Toys worked directly with actors from the Alien franchise to release realistic figures based on select characters they portrayed in the films. NECA has released seven-inch figures based on characters such as Corporal Hicks, Private Hudson, and Bishop. During winter 2014, it was announced there would be multiple figures of Ripley, Sigourney Weaver's character from the Alien films. NECA worked directly with Weaver to develop these action figures, which are the first to feature her likeness.

Roger Luckhurst in his 2014 book on the original Alien film, compared its underlying worldview to that of Aliens stating, "Even if Alien was a piece of leftist science fiction, the core of (its) myth could be inflected the other way. James Cameron's Aliens would be a defiantly Reaganite version of the story—pumped, militarized, libertarian and driven by a staunch defense of the nuclear family."

The special edition was released as part of The Alien Legacy 20th Anniversary Edition DVD box set in 1999 along with Alien, Alien 3, and Alien Resurrection. Both the theatrical version and the special edition were released again in 2003 as part of the Alien Quadrilogy DVD box set along with similar versions of Alien, Alien 3, and Alien Resurrection. A separate two-disc "special collector's edition" DVD of Aliens was released on January 6, 2004, containing the same material as the two Aliens discs in the Quadrilogy set. Additional content in these versions included an audio commentary for the special edition featuring Director James Cameron, Producer Gale Hurd, special effects artists and crew members. The second disc included special features relating to pre-production, production, and post-production. The film was first made available on Blu-ray in the 2010 box set Alien Anthology, before receiving a stand-alone release the following year. Fox released the 30th-anniversary Blu-ray of the movie on September 13, 2016.