There's a lot to think about considering it's purposefully vague. If you didn't walking away from that film with some questions, I wouldn't believe you even saw it. You can read Clarke's book if you really need to know the details, but it isn't necessary. The ride is what's important.
Oh yeah, Solo posted this in another thread that must have gone unread, so I'm gonna post it again:
Well, the whole film is about evolution, as the three acts are broken up as such (and the black monoliths symbolize each evolutionary leap). The monkeys learn to use/make tools, which was the first evolutionary jump. The next jump is man in space. Then when HAL goes crazy, and Dave is forced to shut him down and make it to Jupiter on his own, the final evolutionary leap is made. Dave arrives in the chamber, and begins aging rapidly, and the final monolith appears when he is on his deathbed. The final evolutionary step is Dave (aka man) being reborn as the Starchild, a higher form of intelligence and being, and being sent back to earth.