This is a fairly low-budget movie, but the filmmakers were able to construct an engaging film with their limited resources by relying on clever directing and a solid script. Since all of the rooms in the cube look identical, the entire movie was filmed using a single room. Using only one room could get visually boring, but the director was able to keep things interesting with a good use of lighting and camera angles. The focus is placed on the characters and what they're going through, and the direction emphasizes that with the way the film is shot.
The characters themselves are interesting. They each have a specific role to play not only in the story, but in the cube itself. Each of them has a certain ability that will help them figure out how to escape, and a good part of the movie is spent showing how the characters discover what they have to offer. Their personalities are all very different, some of them bordering on caricatures at times, which leads to some tense conflicts that are more dangerous than the cube's traps. At its core, Cube is a movie about people and how they react to life-threatening situations.
There are also some bigger themes going on in Cube. There's a very clear statement about the figurative machines that drive society and the roles citizens play in that. There are also themes relating to guilt, desperation, deception, and even the meaning of life (or at least how much life is worth). To say much more would spoil the movie, and I think Cube is worth discovering for yourself.
Fans of thoughtful sci-fi will definitely like Cube.