2001: A Space Odyssey is essentially Stanley Kubrick's meditation on what the Space Age (which was pretty new at the time) might mean for the evolution of the human species. The movie also poses the very provocative notion that the evolution of our species was helped along by a vastly advanced alien civilization millions of years ago.
Before 2001, science fiction films had been mostly the province of robots, flying saucers, and bug-eyed monsters. But Kubrick wanted to create "the proverbial GOOD science fiction movie," one that was technically accurate and had a few things to say about the human condition, both past, present, and future. He also threw in some penetrating observations about how technology could be both a boon and a bane to our species.
There are many aspects of this film that are open to interpretation. It was not Kubrick's intention to spoon-feed his audience, but rather to stimulate their imaginations and mythological yearnings. Read some of what's been written about this film, watch it again, and I think you'll end up appreciating it more.
Here are a few links you might find helpful:
I really enjoyed this film, and it is true that the first three acts could be considered a masterpiece. However, the final sequence was a bit of an anticlimax for me. The book did it much better. I can appreciate what Kubrick was trying to do with that final sequence, but I feel he didn't really achieve it.