An exciting beginning to one of the most creative and innovative television programs ever made. This episode strikes a chord because it taps into two of man's greatest fears: autophobia, which is the fear of being alone, and the paranoid feeling that somebody out there is watching us. The episode did an excellent job of creating that terrifying feeling of solitude and how a person can become psychologically unstable eventually in a situation such as this. His fear continues to grow, to escalate until he breaks down completely and cannot take any more.
And of course, we have that twist at the end that has been the staple of "The Twilight Zone". This episode would set the tone for the rest of the series.