Director Don Siegel [Dirty Harry, Escape from Alcatraz] also does a masterful job of increasing the tension as well as the action as the movie develops. The pacing of this film is perfect and the visual effects are subtle but effective. A beautiful film score from Carmen Dragon also enhances Siegel's work and creates a wonderful atmosphere for this film.
Finally, the cast is absolutely stellar with strong performances from everyone. Kevin McCarthy [Innerspace, UHF] is front and center as Dr. Miles Bennell who begins to suspect that something strange is happening in his hometown. The emotional energy that McCarthy brings to his character is fun to watch. It's a total knockout performance. His love interest and partner in action is Becky Driscoll, played by Dana Wynter [Airport]. Wynter give us a self-assured, emotionally stable character that goes way beyond the usual 1950's screaming beauties. It's refreshing to see.
Although I've never seen the 1993 remake, I have seen the other two and both are quite good. This story will probably be remade about every ten years or so because it's that good. If you haven't seen the original Invasion of the Body Snatchers, what are you waiting for?
For more info check out the film's entry in IMDB.