Moore's work especially with Watchmen, show a masterful ability to created a world that is fully realized by provide background information about the universe the story is taking place in. He finds all manners of ways to impart the this information to the reader using interviews with characters, excerpts from articles or even biographies written by these fictitious people. What was so well done was connecting all of these individual pieces to created a narrative that provides a greater understanding of the whole story and the world it is taking place in. It's definitely worth reading.
V for Vendetta is story was a commentary on government affect on society if it becomes to obtrusive and the length on man was willing to go to change things. This story is one that still resonates today with people sporting the Guy Fawkes mask (the mask wore by V) in Occupy Wall St. protest all over the world. The mask is even worn a hacker group Anonymous, who see themselves as web activist.
Batman:The Killing Joke is also a very enjoyable read. In other interviews Moore has said that the art was better than his writing for this story. That's surprising because Killing Joke and Frank Miller's Dark Knight graphic novels are considered as defining works in Batman's lore. If Moore's mediocre work is this good I can only hope my writing will have such substance.
The full interview (24 minute long) can be seen by following this link.
For more information on Alan Moore you can check out the Wikipedia article.
Also another interview Moore gave earlier this year about the Guy Fawkes mask from V for Vendetta appearing at protest. Surprisingly, Frank Miller is mention in this video also.