To discuss movie endings there are inevitable spoilers ahead. Read with caution.
Research any number of “best or worst movie twist” lists and you’ll find sites which both love and hate the “it was all a dream” movie trope. Sometimes it works very well but at other times it seems to highlight a major issue with the storytelling or writing of the movie in the first place.
Many people hate this twist because it feels like cheating. Asking an audience to invest two hours plus of their time into a story which didn’t actually happen can feel like a slap in the face and can often pull the rug out from the audience that want real closure. One such example is American Psycho. Having screwed and murdered his way through the corporate world, Christian Bale’s Patrick Bateman seems to emerge from a dazed, dream-like state, unaware to whether he has actually committed the crimes or not. It not only feels cheap but also manages to get the writer out of the tricky situation of how to end their film after all.
This is when “it was a dream” is done badly. Planned from the beginning, it can be a very good device, with hints and clues thrown in throughout. David Lynch’s Mulholland Drive is seen as a good example of this but on the other end of the scale is when it was clearly a device to get a writer out of a tricky situation. To have a character suddenly awake, sweating, gasping but safe knowing what they just experienced was a nightmare is the writing equivalent of a reset button. Although not a movie, you can’t escape the best example of this which is Dallas, completely rewriting and forgetting a whole years worth of a TV in one scene.
That isn’t to say that it is a twist or storytelling device that doesn’t have some merit though. If the seed is planted well or even ambiguously, it can spark debate which rages on for many years and makes the movie a talking point. Total Recall has been such a movie, with the final scene making many people wonder whether Arnie is actually awake at all.
Take this concept one step further and you could have people writing whole papers on whether a single scene is a dream or not. Inception planted a seed with one simple storytelling device, a spinning top. The final scene manages to be ambiguous enough to make people debate and argue, analyse and scrutinise in the hope that they figure out whether the lead character ever got their happy ever after.
The “dream twist” doesn’t have to be ambiguous though, or all that clever. Sometimes being one of the first to do it well is enough to cement it’s place in the “best movie twist” lists. Nobody is calling it a twist in The Wizard of Oz but nobody claims it ruins the movie either.
Overall, it seems the rule to follow is make sure it is planned from the beginning. The best movies that are “all a dream” can be proven to be that way throughout. The worst are clearly written without that in mind and use it as a “get out of writing jail free” card. Done well, it is a topic of debate. Done badly, it’s Dallas!