You really dont need to know the storyline...you can base your whole essay on the opening sequence (i did and got HSC mark 94). Just say about the symbolic imagery....the Sun being an ancient aztec symbol of fertility, which has been polluted by the rise in technologies (symbolised by the poluted haze which covers the sun).
Also, Tyrell Corps. tower is shaped like a ziggurat. The ziggurat is another symbol of Aztec fertility--a phallic symbol, and the idea is that technologies have altered traditional concepts of sexual reproduction, hence disrupting natural rhythms etc.
Link this to a few concepts and totalitarianism, and you are set.
It is all bullshit...but it is so far fetched that the examiners love it.