Here's my feeling: if you throw everything at a person, as we tend to do, they may be impressed at the complexity of the story, but they're overwhelmed and rarely dig in further.
If you give them a small nibble, then entice them to come further, you're going to see more, you'll pull in many more people.
For example, a friend of mine mentioned that Attack of the Show segment - he knew of Watchmen from me, but seeing that short overview got him excited.
He's really into politics, so he asked me about Nixon still being in power, and rather than get into the massive story, I just gave him a short bit about Doctor Manhattan, how his presence affected Nixon, Viet Nam, and how Watergate never happened.
So my friend wrote back, asking more about Nam and The Comedian - so I gave him a little more information. He was getting much more intrigued finding things out in these little pieces, rather than me unloading everything on him at once.
I think a tiered approach would work - maybe even a single page, heavy with representative graphics, that new users can read over and then click to go deeper.
Here's my vision of how it could work: http://plasmicstudio.com/watchmen/watchmen_overview.jpg
The little yellow icons in the photos can be clickable, to get to the comic's representation(s) of the character.