It's only better if you -- by reading up on convention beforehand -- know which way an edge points; does decreasing thickness indicate an incident node, or the opposite? Not clear on its own.
Umm... that's great for printed materials but how are you going to make that work on a white(black)board or for that matter with a pencil?<p>Not sure I've done many directed graphs in print but I've done quite a few with a marker/pencil/chalk.
While I understand how arrows on the end of the edge is a bad idea, especially if you have a lot of edges on one node; what about having arrows blended in the edge itself?<p>Something like this (beware the ASCII art):
o---->----o
I really like the gradient use on the edges. That, along with the taper, allows a reader to easily see the direction without having to follow it till it hits another node.
Interesting, I feel for "trained" users who use directed graphs for work this is a valuable technique. But even the researchers admitted it is not obvious which way the flow goes. So I don't think it would work well for advertising or public presentations.<p>The research paper makes interesting reading, and how often can you say that!
I have a graph theory based application in the Android market, "Edgy," and I doubt that I would switch to this. I think once you get used to it, it is perhaps clearer, but I think there are many opportunities for styling and weights that may increase clarity without having to do something that is not expected. If this catches on, of course I'll probably go that way, but as for now, I haven't even seen many, if any, graphs use this.