I understand that it is a cult movie and for its time it is incredible but it is not so slow and has so few dialogues, that I fell asleep a few times and make it difficult to follow. I understand that there are two plots, the one of the robot that goes crazy (from which many works like Portal) that is cool and then the one of the monoliths and the different evolutions of human and alien life. the problem is that to understand this last one I had to watch a video and it is not something I like to do :( still maybe I recommend it if you are a professional cinephile like me.