North by Northwest is a classic suspense movie, a film that is unparalleled even today in terms of producing an optimal combination of plot, humour, action, and intrigue without resorting to cliches.
Directed by Alfred Hitchcock, the master of suspense, the style of film making is composed of a few key traits that results in the movie being ranked high as one of the greatest films in my book: The plot is novel and there are plenty of plot twists that keep the audience constantly engaged. Each of the twists is calculated (or mis-calculated) precisely and at every direction (or mis-direction) the audience in told only the barest minimum they need to know. The protagonist gets out of difficult situations in incredibly imaginative ways, without insulting the intelligence of the audience. A lot of the action is "hidden"---for example, a single sentence at the end by the protagonist explains how he escaped from being held captive at gun point, without actually depicting what happened. As a result, the rest of the action (like the classic scene involving Mount Rushmore) is prolonged in an almost-excruciating manner. All this makes for thought-provoking suspense. Not only do our minds work trying to fill in the (obvious) gaps while we keep guessing as to what will happen next, but we also have to wait longer when we're witnessing an action sequence that is occurring in the movie.
The film begins by dropping us right in the middle of confusion: Roger Thornhill (Cary Grant), a Madison Avenue business executive, is mistaken for a George Kaplan, supposedly a government agent, by Phillip Vandamm (James Mason), a spy. Thornhill insists that Vandamm has the wrong man, but Vandamm is unconvinced and decides to kill him anyway. Thornhill escapes, but ends up on the wrong side of the law. While trying to clear himself, he digs himself deeper into the hole resulting in both the police and Vandamm's thugs hot on his pursuit, resulting in a 3000-mile cross-country chase. While on the run, he bumps into Eve Kendall (Eva Mary Saint) who offers to help him but is really in cahoots with Vandamm. This basic plot is set in a backdrop of international espionage: nothing is quite what is seems and it seems The X Files' watchword "trust no one" is extremely apt here. Thornhill is caught between feelings for Eve, risk of death from Vandamm's goons, and a U.S. government agency with a vested interest in continuing the charade. How all this is resolved in a clear and consistent manner is what makes this script and direction so great.
However, writing and direction alone, as imaginative as it is here, do not make for the greatest movies. All of the actors do an excellent job in realising the potential in the script: Cary Grant and Eva Marie Saint offer rock-solid performances. Martin Landau is a great villain as Vandamm's henchman. James Mason's face as he learns of the Gestapo trick used by Eve and Thornhill changes from surprise to shock to incredulity to rage. This is acting at its most brilliant. The score (both in terms of composition and quality) also complements the nail-biting suspense in just the right manner.
Few films can be a showcase to the art of great film making (considered from a purely entertainment perspective). North by Northwest is one of them. I recommend renting it and watching it on as large a screen as possible.