While initially, the film was very much underrated after the success of The Sixth Sense (compounded by the fact that both films have Bruce Willis as the lead), Unbreakable is a brilliant film that was ahead of its time. Following Willis' character David Dunn, who is the only survivor in a horrible train crash, and Elijah Price (played by Samuel L. Jackson), a man born with a rare bone disease that leaves unimaginably fragile, the film has these two characters coming together to try and explain how Dunn survived.
The film constantly references comic books, through stats at the start of the film, and with Price's obsession with them, and how they are a representation of the world we live in. Even the colour schemes and dialogue are somewhat similar to a comic book, with rather limited use of speech, instead focusing on visuals, and each main character possessing their own colour palette (Price is always wearing or surrounded by purple items, whereas Dunn is surrounded more by green).
I want to avoid going into spoilers (even though the film is coming up to 19 years old) because the film still stands today as a great film. It doesn't feel old. It has aged superbly, and if you haven't seen it yet, I would greatly recommend checking it out before seeing Glass at the theatres.
With Dunn as the protagonist of the film, what is missing throughout the film in the antagonist, and it slowly builds as it searches for this missing character, taking moments throughout the film to compare with comic books describing the characteristics of villains throughout.
Bruce Willis does some of his best work in Unbreakable, as the calm and collected man that is, unfortunately, going through marital issues. Samuel L. Jackson gives a performance that shows his forgotten ability to perform dialogue that isn't just leading him towards saying "motherf**ker" as many times as possible.
A brilliant origin story that doesn't rush into things. It doesn't fully explain things either. It leaves it up to the audience to come up with its own conclusions. The final scene in the film provides a twist, that while it feels unwarranted, beautifully sets up the antagonist for Glass. If this film was made today, it would have made one hell of a mid or end-credits scene.
Unbreakable is tense and suspenseful, despite a near complete lack of action. Fantastically shot, and it still stands up to scrutiny today. A film that I would definitely recommend.