When I first watched 2001:A Space Odyssey I was eight, which is probably a shame because I was bored out of my mind, not having the patience to endure it's almost three hour length nor the intelligence to understand the rampant symbolism and themes. But now, I can see it as the masterpiece it is. Certainly you have to be in the right sort of mood to watch this movie, but if you are it is a beautiful experience. I cried.
If anyone is unsure about the cryptic ending, let me offer my interpretation. The monolith is an alien technology that speeds up evolution. We see this as the monkeys stroke it and suddenly have the knowledge to use weapons, which puts them lightyears ahead of their peers (literally, as we see that those apes have put satellites into space). On the moon, the men also touch it (we don't see what happens to them, but I'm thinking giant floating fetuses) We later see the monolith floating out in space near where Dave and HAL are. The stargate scene (the trippy one) is literally the experience of quickly evolving. The end where we see the giant floating fetus is the next evolutionary leap forward (for some reason). That's my interpretation anyway.