This movie should never have been remade (though I haven't seen the Christopher Reeves version). We watched Disturbia a while back and it is a movie that will forever spend a night in the box. Alfred Hitchcock's masterpiece doesn't have to create a gory film or a terrifying background for the killer, the suspense around the murder is enough. When you start displaying the evil (serial killings, gore, etc.), it becomes either too frightening or too cheesy to enjoy.
On that note I really enjoyed this original version. It all takes place in an apartment living room and is never slow or dull. This type of movie isn't made to inspire, but primarily to entertain, and I believe it achieved it's purposes.
Jeff is a nosy, crippled man with nothing better to do than to involve himself, uninvited, in the lives of his neighbors. He ends up neglecting his own real-life relationships for his imaginary ones he forges through a telephoto lens. It is very unrealistic in the fact that he is able to understand each neighbor's situation by simply observing them and never interacting with them. This may be the purpose of the film to display the risks of being a busy body and the importance of focusing on strengthening real life relationships.
Lisa did end up relinquishing her efforts to dissuade Jeff from pursuing his new hobby of prying and immersed herself in it, though she denounced it at first. This was a selfless act that showed her devotion to him and her willingness to bring their relationship closer proving she really was interested in marriage (which was a qualm Jeff had in the movie with regards to whether or not she was ready or not for marriage).