The first two films are much darker and more serious than the later sequels. Before the third film, Freddy Krueger was very much a monster, and he wasn't the least bit humorous; when he did speak, it was meant to scare his victims rather than have a laugh at their expense. The early films also have some strange quirks of their own:
In the first film, the characters and the credits identify the killer strictly as Fred Krueger (he's only called "Freddy" in the Ironic Nursery Tune), he only kills four people, and it wraps up with a Gainax Ending that raises the question of just how much of the film was real versus what was in Nancy's head.
The second film, Freddy's Revenge, is even weirder. The plot revolves around Freddy possessing a teenage boy (complete with a Body Horror-filled transformation scene) in order to re-enter the real world, something that never comes up again in later films. It also has mountains of Homoerotic Subtext in the protagonist Jesse's character, his "relationship" with Freddy, and some of the kills (most infamously the gym coach's death).
For a monster that is now-infamous for its blinding-fast speed, the first Alien is shown almost exclusively moving slowly and ominously. We only see it move quickly for brief instants when it strikes, just before the shot cuts away. Later films in the series establish the aliens hustling about.
The first Austin Powers was slightly darker in tone than its sequels, parodied James Bond tropes more directly, and had those short segments with Austin dancing to music in-between scenes.
In the first Back to the Future, Marty's central personality flaw in the sequels—his habit of submitting to peer pressure when people call him "chicken"—isn't anywhere in sight. Indeed, the one time we see him being verbally taunted—when Biff's gang makes fun of his jacket—he easily ignores it. His motive for confronting Biff later is entirely a sincere desire to protect his mother; there's no evidence that he cares what they think of him. Hand Waved by Word of God, who claims that the new timeline created a Marty with a more privileged background, causing the personality change.
The Bourne Identity feels very different in tone to its sequels. The Bourne Supremacy and The Bourne Ultimatum are contiguous to the point that there is no time-cut at all between the last scenes of the second film and the first scenes of the third film (not counting the Bourne-in-New-York-scene, a Supremacy note which is "also" tied up in Ultimatum...). But when you have recently seen Supremacy and/or Ultimatum, it can come as a bit of a shock to rewatch Identity and realise how different it is, though it was setting up all the Bourne tropes the later films played on. Notably, the soundtrack is a very different beast, employing techno-ish and poppy background music. Damon's Bourne is also surprisingly chatty and smiley compared to his later silent stoicism. The editing takes a different approach completely, and the camera work is free of the Jitter Cam that defined the sequels. Most of this change in tone has to do with the first film being made by a different director to its sequels, and the fact that there was several years' gap between its release and the release of its first sequel.
His first feature film, Tillie's Punctured Romance, not only does he not wear the Tramp costume, he's the bad guy. A partial explanation is that this film was directed by Mack Sennett for Keystone Studios, and Chaplin would not gain full artistic control of his career until he left Keystone not long after.
A similar example from Chaplin's time at Keystone being the short Mabel At the Wheel (starring and co-directed by Mabel Normand) in which Chaplin not only plays the villain but in contrast to his "Tramp" persona is seen wearing a top hat, frock coat and goatee-like beard (apparently in imitation of Ford Sterling, whom he'd been hired to replace).
The Tramp's first appearance on film was Kid Auto Races at Venice, where the Tramp does not display much of his trademark personality. He's simply a bystander at a race who wants to get on camera and keeps wandering into the shot.
The original Death Wish is a gritty, realistic, look at urban decay and out of control crime in major American cities during the era. The movie was such a hit largely because it embodied the feelings of many honest citizens at the time. In the end there is no dramatic showdown with the men who killed his wife and raped his daughter, they simply disappear into the city and Paul will never know who they were. There's little graphic violence, but what there is is very disturbing. Nothing in the movie could be defined as gratuitous. When the schlocky production company Cannon Films bought the rights eight years later, they began releasing sequels that were more or less exploitation and dumb 1980s-style revenge fantasy action films.
The original The Evil Dead (1981) is more a Gorn horror film, rather than the horror comedy of Evil Dead 2. Also none of the other cabin members besides Linda is mentioned in the other films. Ash is far from the Catch Phrase spouting, Bad Ass and Jerk Ass we see in the sequels, instead being a rather bland Final Girl played by a guy. The Necronomicon doesn't have that name and the look of it is completely different from the other films. And lastly, in a subtler example, the Deadites (which aren't named as such until the second movie) are originally just pissed off that the teenagers awoke them from their eons-long sleep, whereas in the sequels they implicitly want to Take Over the World.
The original Final Destination includes some more overtly supernatural elements that were left out of the sequels. Among them are an implied psychic link of sorts between Alex and Clear, the foreboding presence of gusts of wind from nowhere right before a death scene, a smoky black shadow that appears on reflective surfaces when Death is coming for someone, and a shot of Death supernaturally "covering its tracks" after Tod slips on the water leaking from his toilet, causing his death; the water impossibly recedes under the toilet to "hide" itself and make it look like a suicide. The last point is a rare example within the film itself. Filmmakers had planned for Death to cover its tracks throughout the film, but after the first death they changed their minds to simply have the rest as accidents.
In the original Friday the 13th (1980), Jason not only isn't the killer, he doesn't even appear save for a dream sequence. He doesn't get his trademark hockey mask until Part III. Also, in Part 2, he's considerably less physically imposing than subsequent movies.
In the original films with Jason as a killer, he was alive rather than the indestructible undead human of later films. In the second and third films, he would run after his victims, back away if someone came at him with something dangerous, and would sometimes even grunt in pain. Surprisingly, despite not yet having his undead killer status yet in Friday the 13th: The Final Chapter, his behavior is actually closer to as it is in the later films.
The original film is noticeably different from its sequels and remake in a couple of ways; there's much less blood and killing, and it focuses far more on suspense. Starting with Halloween II (1981), Michael's kills were bloodier and more elaborate to more closely match the numerous slasher movies the original had inspired.
In the first movie, Michael has no apparent motivation; he's just "pure evil" and kills on instinct. In Halloween II (1981), it's revealed that Laurie, his main target in the previous film and that one, is actually his sister. From then on out, every movie he appears in includes an element of him specifically stalking a family member. Taken to its illogical extreme in the sixth movie, which reveals Michael suffers from a druid curse that requires him to kill off his entire family.
Throughout the films, more and more areas are added to Hogwarts, making the Hogwarts of the first film almost a kind of bare-bones version with, for example, nothing between the back of the castle and Hagrid's hut but a field of grass.
In the first two films, Professor Flitwick is an elderly-looking midget◊. From the third onward, he became a small man with brown hair and moustache◊. It was so unexpected that quite a few people joked that he now looked like Hitler. (the story is complicated: as Flitwick wouldn't appear in Prisoner of Azkaban, actor Warwick Davis was instead offered a cameo as the chorus conductor - credited only as "Wizard"; through Retcon, that guy became Flitwick in the fourth movie). Combined with that is the fact that J. K. Rowling wasn't entirely happy with Flitwick's original appearance. The original movie Flitwick looked, in her opinion, a bit like a Goblin, while she had always pictured him as just a very small man.
Filch. In the Columbus films, his characterization was very much in keeping with his book counterpart; from the fourth movie onward, they used him as comic relief.
There's also a drift away from on-location shooting and towards soundstages. At the start of the series, they couldn't afford to build every room in Hogwarts, so there were only a few purpose-built sets and most of the Hogwarts interiors were filmed at various castles, cathedrals, and universities. As the series went along, they built up more and more sets, which was coupled with improvements in CGI technology. Philosopher's Stone was filmed at locations all across Britain, while Deathly Hallows, Part 2 was filmed almost completely at Leavesden Studios. Some places that were originally filmed on location were reproduced as sets later in the series, often accompanied by changes in design — compare the hospital wing in the first movie to the hospital wing in the second movie onwards.
In the first movie, the students wore pointed hats with their uniforms during formal scenes in the Great Hall (you'll recall these hats being tossed in the air when Gryffindor won the House Cup). The hats disappeared in the second film and were never seen again. This is probably due to infrequent mentions of hats being part of the school uniform in the books. Doubtlessly, they were dropped because they looked ridiculous.
In the first film, emphasis is put on the fact that the staircases can change path, and this does have an effect on the plot. In the second and third films, this is relegated to background scenery, and by the fourth they seem to have gone altogether.
The first movie puts a lot more focus on Harry's life with the Dursleys, probably to help get a feel for how much Hogwarts improves him. In the later films, since the audience already understands, they only make up the first ten-fifteen minutes... if they're even present at all.
Also in the first movie, the Dursleys were portrayed as somewhat over-the-top antagonists, with practically no redeeming features who seemed to take almost sadistic pleasure out of torturing Harry. While no more likeable in the later films, the Dursleys (at least the parents, Dudley always remained a bit of a jerk) became a bit more human in their portrayal.
The Hunger Games had a much different look for District 12 and the Capitol than we would see in later installments. For instance, 12 was portrayed as much more rural and barebones, while Catching Fire would show far more mechanization.
The first film featured humans and portrayed all of the animal characters more realistically (they walked like the actual animals always, and could not speak to humankind). In the sequels however, the tone turned Lighter and Softer, all of the humans are written out of existence, and all of the animals are now the main inhabitants of the world.
The original movie had David Newman to compose the score, while John Powell composed the score for all the sequels. As a result, this makes the original movie's soundtrack stick out from the sequels like a sore thumb.
The 1954 film Gojira, which kick-started the Godzilla franchise, is a surprisingly dark (and seriously scary) horror film rather than a campy monster movie. Because Godzilla is the only monster appearing in the film, the focus is on the humans' response to his rampage rather than on a battle between opposing monsters. Also, Godzilla is a metaphor for the horror of nuclear weapons and is unambiguously presented a villainous monster incapable of reason or sympathy, rather than the Noble Demon and defender of humanity that he evolved into as the series went on.
The first entry into the Marvel Cinematic Universe had a few issues which would be retconned out in later films, mostly regarding SHIELD. Agent Coulson introduces himself as being from the "Strategic Homeland Intervention Enforcement and Logistics Division," then saying they're "working on shortening the name." This suggests that it's a fairly new organization but was likely to ease in moviegoers who were unfamiliar with SHIELD, as later installments would show that SHIELD has been around for decades.
It also claims Tony Stark is only in his 20s. Later films would establish him to be at least a decade or more older than that.
Terrence Howard plays Lt. Colonel Rhodes, while Don Cheadle would take the role for later Marvel films.
If you watch Dr. No after other James Bond films, it'll be a shock: it's a hard-boiled detective story instead of a spy action thriller - mostly because the budget was low. The fight scenes and car chases are rare and short; the only gadget per se is a mook's Cyanide Pill (Q - here, Major Boothroyd, and not played by Desmond Llewellyn - only appears to change Bond's gun). Even the opening sequence is all wrong. It starts with a series of weird electronic beeps, and the familiar theme doesn't play until Bond shoots the gun barrel, and it starts on the wrong cue (the big dramatic part of the song, instead of the actual intro). Then the barrel wiggles down to the bottom of the screen and the opening scene wipes in from— oh? No, it moves on directly to the opening credits while still playing the Bond tune, over some colorful dots appearing all over the screen. Then it jarringly switches to some upbeat salsa music (not a theme song including the movie's title) over some colorful silhouettes of people dancing for a minute or two, when it again suddenly switches to a salsa rendition of "Three Blind Mice" over the silhouettes of the title mice, which then fade into the actual opening of the movie. To call that opening schizophrenic is being a little too kind to it. In fact, the music-video Bond titles didn't appear in their best-known form until Goldfinger.
Both Dr. No and From Russia with Love featured Bond flirting with Sylvia Trench early in the film before being called away for the mission. This was intended to be an ongoing Running Gag, but was dropped after the second film. The romantic tension would then shift to Bond and Miss Moneypenny.
Roger Moore in his first outing as Bond is much colder and darker than the comedic tone he would be remembered for.
The first film in The Land Before Time series films is actually the only one that is not a musical. It also has significantly higher animation quality and a much darker tone. Don Bluth, anyone?
The first Lethal Weapon movie, before the series embraced its comedic elements, is much darker, with moody sax music, and a bit of a Film Noir vibe.
The first Mad Max movie is very different from those that followed. It is not postapocalyptic, and Max spends most of it as a happily married family man with wife, child and job rather than the lone nomadic warrior of the wastelands he later becomes. The film is also very different in tone, relying more on slowly building suspense with only occasional, brief action sequences.
The three penguins that aren't Skipper are clearly different from each other in the first film, but as a whole act more as goofy slapstick secret agent parodies. It wasn't until the second film that their personalities started to get fleshed out more.
The first film had a dramatic moment near the end, but overall focused much more heavily on fast-paced humor and pop culture references than the (somewhat) more emotional later films. Also, it takes place in Madagascar.
The original Poison Ivy was a character-driven thriller with A-Lister Drew Barrymore in the title role, and (here's the kicker) no female nudity at all. The following three sequels were a loosely connected series of erotic dramas starring B-List actresses, known for their gratuitous sex and nudity...and not much else. In an odd subversion, though, the original is probably the most well-known of the four.
The original The Producers, being Mel Brooks' first movie, is a bit straight-forward compared to his later comedies.
It's the only Indiana Jones film without the name "Indiana Jones" in the title. Though recent boxsets and home releases label the film as "Indiana Jones and the Raiders of the Lost Ark."
While it does have its share of gags (such as the famous shooting-the-swordsman scene) and one-liners ("It's not the years, honey, it's the mileage"), it is overall a lot more serious in tone than any of the later films, which feature outright slapstick and screwball elements.
It goes much further than any of the later films in imitating the look and style of 1940's serials and adventure films such as The Spy Smasher.
The Rambo films are known as popcorn action flicks about a One-Man Army named Rambo mowing down armies of Dirty Communists with a heavy machine gun. The first film, First Blood, is an anti-war film about the dehumanization of soldiers, which involves a Shell-Shocked Veteran named Rambo becoming a fugitive from the law after being mistreated by lawmen in the country he served, tormented to the core by his traumatic experiences fighting the Vietnam War. This Rambo goes out of his way to avoid killing, slaying three police dogs in self-defense because he had no other option, and subduing the rest of his pursuers non-lethally because he just wants them to leave him alone. The only person to die is an Asshole Victim who is killed completely by accident, and whose death has major plot significance unlike the Mooks of later films. When he's brought into Tranquil Fury / Unstoppable Rage by an explosive attempt to kill him and gets a heavy machine gun, Rambo uses it to destroy property and disable an enemy but still doesn't use it to kill anyone. The one time he seems ready to kill someone, he is met by his former commander who successfully talks him down. It ends on a famous two-part speech about the trauma and mistreatment of veterans delivered by a Rambo who suffers a mental breakdown midway through and starts crying. That's not even mentioning that the film is based ona book that's not only more violent than the film is but has a much less sympathetic take on Rambo than the film does.
Saw. In the first two films, Jigsaw is a brutal Serial Killer with an interesting MO. Also, the first film contains very little gore, and the second only contains a lot of blood, but nothing too explicit beyond that. The Torture Porn that the films became known for didn't really start until the third film, at which point Jigsaw was toned down considerably into a very deranged man with a tragic past, but with his heart in the right place. While still a psychotic villain, he is no longer like the first two films. That role, instead, gets taken over by his apprentices, especially Hoffman.
W.C. Fields became famous for his portrayals of bitter old misanthropes who hated children. But in early starring vehicle So's Your Old Man, he's a loving, if bumbling, husband and father. Additionally, he's quite a bit thinner and more nimble than he was in later films, and he sports a bushy mustache in this film.
Star Trek III: The Search for Spock was the first Star Trek production to feature the full Klingon language, and so a lot of the word pronunciations are different to how they would sound in TNG onwards — for example, listen to how Kruge says Qapla' (with a more phonetic sound) just before Torg's boarding party leaves for the Enterprise. The most common explanation for this among fans is that Kruge just has an odd regional accent.
Star Wars: Episode IV - A New Hope has a number of elements that can seem strange in comparison to the series as a whole.
The film has a number of plot elements that were changed or outright retconned in the later canon, with Anakin and Vader as different people, the Jedi and the Force being widely considered a myth, etc. A video showcasing all this exists here.
Darth Vader showed far more emotion when delivering his lines than he would in the sequels - he actually showed anger and rage when tearing through the Rebel ship and later showed amusement when Force choking an uppity Imperial during a meeting.
The lightsaber battle in Star Wars Episode IV - A New Hope is quite stiff and awkward compared to the more dramatic and gymnastic swordfights in later installments. According to Mark Hamill, the original lightsaber props had motors to rotate the "blades," making them too heavy and dangerous for any impressive flynning. Also, Obi-Wan's lightsaber "flickers" in mid-battle, while most subsequent lightsabers do not.
Jabba the Hutt wasn't a slug monster in the original screenplay, he was supposed to be a furry creature like Chewbacca, and the only scene in the original movie where he appears was cut. It was restored in the Special Edition, but Jabba appears much more mobile and less bulky in his CGI form than his puppet form from Return of the Jedi. This is because he was inserted into the footage over the stand-in actor, who was much shorter than Harrison Ford. Han calls Jabba a "wonderful human being," a sentiment that seems quite odd when said about a slug (although most viewers of the Special Edition assumed that Han was just trying to be sarcastic). Additionally, "Hutt" was not intended as a species name but a title, much like a mafia boss would be called Don.
Vader's suit was dirtier in the first movie and the metal part on his chest was behind the two cloth strips instead of in front of them. The eyepieces on his helmet were also tinted a very dark red before switching to solid black in Empire and beyond.
In the original cuts of Episode IV, conventional English script could be seen, most notably when there's a closeup of a control panel showing the Death Star's tractor beam power dropping to zero (the words POWER and TRACTOR BEAM are clearly visible). In Episodes V and VI more care is taken to use alien-looking script, and the remastered versions of Episode IV substitute the visible English with this same alien lettering.
Obi-Wan refers to Darth Vader as "Darth" during their fight rather than "Vader", as if it was his first name instead of a title.
While the scene where Owen buys C-3PO from the Jawas suggests that the droid is multilingual, it is not until Empire that he claims to be "fluent in over 6 million forms of communication."
When Obi-Wan cuts off an alien's arm during a bar fight, you can see blood drip out of the limb. In other movies, lightsaber wounds are instantly cauterized by the blade, keeping blood from flowing out.
The original Teenage Mutant Ninja Turtles movie (1990) is a good deal grittier than its sequels, with an overall more serious tone and fewer comic-book gimmicks. Yes, there is plenty of humor, but it is there only to underscore the brooding nature of the piece rather than to exist for its own sake. Also the jettisoning of most supernatural elements: Master Splinter and the Turtles themselves have a supernatural origin, but their allies and enemies are all ordinary human beings. Not until The Secret of the Ooze (1991) do we get to see used as villains the bizarrely mutated beasts for which the cartoon series and the original comics had become famous.
The first Terminator film is really weird compared to the ones that follow. Chief amongst the differences is that it's a Horror-Action hybrid with much greater emphasis on the Horror. It also has a much lower budget than the rest of the films, making it look somewhat dated in special effects. And finally, the Time Travel plot mechanic uses a very closed and fatalistic Stable Time Loop while the rest of the movies run amuck with the Timey-Wimey Ball.
Watching Toy Story 15 years after it was originally made, while the composition of the elements is still impressive, it is noticeable how certain textures (hair and fabric) are left rather ambiguous and that the faces of human characters other than Sid are often out of frame. This was due to the technology not yet being at point where it could render organic things realistically: it wasn't until The Incredibles that they took the plunge and made a film about people. The film is also remarkably low-key compared to the bombastic flourishes of later films in the series.
On the subject of Pixar, Toy Story doesn't have their Vanity Plate shown before the film (although it does appear after the credits). Instead, the Walt Disney Pictures logo, rather than fading to black, actually transitions into the movie proper, by having the camera pan away from the castle until it fades into the wallpaper of Andy's room.
Transformers is a more straight-forward story with a relatively short number of robot characters (Sequel Escalation and Serial Escalation were heavy in the two movies that followed). Also, while Bumblebee drops Sam and Mikaela out of his vehicle mode before transforming into his robot mode to fight Barricade, the sequels have the transformations fast enough to safely eject any passengers and quickly convert into robot mode in one quick go.
The first film had Cybertronians bleed blue-green Alien Blood (most likely meant to be Energon). The sequels replace it with a red substance that may or may not be real blood (they're alien robots, remember).
If your knowledge of Twilight comes from Pop-Cultural Osmosis, you'll find the first movie awfully strange. It's essentially a low-budget indie (a very successful one) and it feels like it. There are only the most basic special effects and it generally just feels "small". In contrast, the sequels had higher budgets, so they feel bigger and have a blockbuster "sheen" which the original lacked.
Kitty Pryde (Shadowcat) appears in all three X-Men films, is notably discussed in the US Senate in X1 and referenced by Xavier to the President of the United States in X2, but her on-screen appearances are very brief, almost cameo-sized, and she's played by different actresses in each. In X-Men: The Last Stand, she finally becomes a main character with whole sequences from her perspective, and is portrayed by Ellen Page. The first film also features a different actor as John Allerdyce (Pyro) in a brief cameo. John becomes a main character with a different, lasting actor for the next two films.
The first Mission: Impossible film: Despite the movie being the Trope Namer for "Mission: Impossible" Cable Drop. which in turn would set the bar for the high concept scenes and stunts of the sequels, the first film is VERY different in tone from them. There's very little in terms of action scenes until the end - even the titular "Mission: Impossible" Cable Drop scene is more tension than action or complex stunts. Ethan's character doesn't have that "larger than life" reputation and presentation the other films give him. It's a much more quiet and psychological film whose tone does clash with its sequels, who would become more known for their action and stunts, when watching the series back to back.