Mr Ghostface said:
Well, of course it doesn't introduce us to anything, it ISN'T the first movie in a series. It's the fourth. Hence it's a prequel, meaning it was made after another movie but it takes place before. It assumes knowledge of the previous movies. Just because it takes place before doesn't mean it has to begin all over again with introductions to things that virtually everyone going to see it already knew about.
No one in 1999 was going to see The Phantom Menace wondering what it was about. They went to see it because it was a new Star Wars movie. So the introduction to the universe would be unnecessary.
This is all well and good, but Lucas expects people to start with TPM now, not ANH.