Audiences love plot twists - so much so, in fact, that they often end up giving a movie way more credit than it actually deserves if it culminates on a crazy or unpredictable twist. After all, it's the element they end up thinking about when they leave the theatre; it's the part they'll remember when somebody asks them about the film.
But a truly great film is made up of dozens of great scenes, and a plot twist can often dupe us into forgetting that. Not that it isn't possible to have a great film that also relies on a plot twist; Se7en, Fight Club and Oldboy are all films made endlessly rewatchable because they don't need their associated twists to be awesome - they're made up of one great scene after another, regardless of the final denouement.
There are some "great" films, however (and, yes, notice the quotation marks), that lack the relentless brilliance of the aforementioned films because they are so very reliant on their plot twists. In retrospect, these twists are likely to be the one aspect you remember about each film, whilst the rest of the narrative lingers hazily in your mind as an unfamiliar blur of forgettable, somewhat interchangeable scenes.
You have to ask yourself: how great can a film be if all you can really remember about it a few months later is its plot twist?