Make a list of seminal movies from the 1990s, and "The Matrix" is likely to appear on it. This neat behind the scenes video shows how the film achieved one of its most famous effects.
Known as "Bullet Time," the effect involves a freezing of or slow motion unfolding of action while the viewpoint changes. This was achieved by rigging up many stills cameras set in some sort of predetermined pattern (this was conceived of in a simulation to help envision the audience's viewpoint) and timed to go off in a very precise sequence. The filmmakers would then interpolate frames to make movement smoother.
Of course, nowadays, such an effect might be done entirely with computers, but seeing it done with a practical setup is majorly cool and shows off the large amounts of planning and ingenuity that went into the effect. I remember my 12-year-old self being blown away by the effect when I first saw the movie. You can see the original bullet time scene below:
Though "The Matrix" was not the first to use the effect, it made it wildly popular, as it would end up appearing in many other movies, television shows, and even concert films.