But occasionally – just occasionally – the stars align and a sequel can end up being even better than its predecessor, even if that original seemed as though it was the best film ever made. Here's our list of shining second-goes...
1. The Dark Knight (2008)
The leap in quality between 2005's Batman Begins and this brutal, unforgettable sequel is astonishing.
Batman Begins merely set the scene: Moody, confident and brave, it paved the way for a film that wasn't scared to take a comic-book subject and turn it into a searing psychological drama.
Heath Ledger's tragic death grabbed headlines, but his twitchy, terrifying take on The Joker in The Dark Knight would have cemented his place in the pantheon of great cinema villains regardless.
2. Evil Dead II (1987)
Okay, so this was essentially the same film as 1981's Evil Dead. This time, however, there was an actual budget (gasp!), and the filmmakers were buoyed by the knowledge that there were people out there who enjoyed their bonkers mixture of gore and the grotesque as much as they did.
Containing more blood, guts, dismemberment and, yes, laughs than the original, Evil Dead II set a new, disgusting bar for all horror movies to follow.
3. Before Sunset (2004)
After a one-night stand in Vienna in 1995's Before Sunrise, Julie Delpy's Celine and Ethan Hawke's Jesse meet again in Paris nine long years later.
Filmed in real-time as they rambled through the streets, the actors mostly improvised the script and their charisma from the first film shone even brighter. What gives Before Sunset the edge on its delightful predecessor, however, is that here the characters have lost some of their innocence; there's a dark, bittersweet edge to their reunion.
Poignant and endearing, it's no wonder we got to meet these two again in 2013's Before Midnight.
4. Aliens (1986)
A tough call, this. Is Aliens actually better than its predecessor Alien? They're certainly very different.
The original Alien was a horror film; the follow-up Aliens is an action movie. But both feature that cold, crawling, menacing dread, and both have seared themselves into our psyches. And Aliens is basically Alien dialled up to 11: More monsters, more characters, more action.
Sigourney Weaver's Ellen Ripley is a reluctant hero in Alien – here, she's a divine being – every inch a true icon of cinema.
5. Indiana Jones And the Last Crusade (1989)
Raiders of the Lost Ark: One of the finest films ever made. Its sequel? Not so much. In fact, Indiana Jones And the Temple of Doom, despite boasting that memorable rope-bridge sequence, didn't live up to its predecessor at all.
But then along came Indiana Jones And the Last Crusade with the holy grail – a flashback sequence in which we see how young Indy found his hat, stunt-work that has rarely been bettered and, yes, Sean Connery. All was right with the world again.
6. Star Wars: Episode V – The Empire Strikes Back (1980)
We're not saying that A New Hope was rubbish. But – even if you sat in your local fleapit in 1977 and decided that Star Wars was the best thing that had ever happened in your entire life – chances are you went back for the sequel in 1980, and realised that no, The Empire Strikes Back is it.
AT-ATs! Space slugs! Han Solo turned into a rock! Darth Vader is Luke's father! A freakin' cliffhanger ending! In short, Empire was more assured than the film that spawned it – a bolder, braver film with deep emotional resonance.
7. Star Trek II: The Wrath of Khan (1982)
Star Trek: The Motion Picture didn't exactly set the world on fire in 1979 – slow, cold and stodgy, some even nicknamed it 'The Motionless Picture'. It made money, however, and so a sequel was inevitable; but how could it be better?
A complete revamp in The Wrath of Khan saw more colour, more humour, more action and more chest (Ricardo Montalban's Khan-pecs almost deserved their own film).
The first Star Trek movie tried to be a 2001-style psychological drama; the second was a tense, Shakespearean revenge thriller. And it was brilliant.
8. The Lord of the Rings: The Two Towers (2002)
There were some who found The Fellowship of the Ring too cutesy – all that skipping through the Shire and hurrying through forests with a beardy old man didn't float their boat, despite some excellent Balrog-and-orc-battling.
But if Fellowship was someone tickling your bare Hobbit feet, The Two Towers was an Uruk-hai punching you in the face. Hard. The Battle of Helm's Deep deserves to stand alongside the fights in Lawrence of Arabia, Zulu and Saving Private Ryan as one of the greatest bust-ups ever filmed.
9. Terminator 2: Judgement Day (1991)
The original Terminator cost $6.4m and grossed $78m worldwide. With returns like that, it seemed only fair to make the sequel a little flashier... And thus, $102m later, we had one of the greatest sci-fi movies ever made.
Using pioneering CGI – Robert Patrick's metallic, oozing T-1000 had audiences staring at linoleum tiles suspiciously for years – and switching Arnold Schwarzenegger's cyborg from 'bad' to 'good' mode, Terminator 2: Judgement Day was every inch an action blockbuster for the ages.
10. The Godfather Part Two (1974)
Everybody and their dog knows that The Godfather is a stone-cold classic, right? But there's also no denying that The Godfather Part Two is even more important, delving into the background of the first film's most memorable character, Marlon Brando's Vito Corleone.
A pre-Taxi Driver Robert De Niro made his name in the flashbacks, while Al Pacino, in the main story, cemented his credentials as one of the best actors of his generation. Cinema at its very finest.
