Reasons why this movie is great :D

1.) Very good story, despite the era it was written in.

2.) Good acting from everyone.

3.) Robby the Robot, need I say more?

4.) Reasonably good special-effects, if a bit dated. (We will not speak of the cartoony Id monster).

5.) Beautifully done movie sets and matte paintings for the planet.

6.) The romance between Altaira and the captain.

7.) Good misdirection on who the real villain is.

8.) A very good use of the concept of "ancient aliens" for the story.

9.) An interesting view on Freud's concept of the unconscious mind (one of the few things he found in his studies that hasn't been disproven or lampooned).

10.) Knowing that this film was a major source of inspiration for one Gene Roddenberry, creator of the 1960s tv show, "Star Trek," that would spawn a cultural phenomenon.