Holy cow, there's a lot of information there! This graphic more or less amounts to a crash course in the fundamentals of US History.
At risk of distracting from the beauty and depth of this "comic," one trend I found interesting was the increasing dominance of the "far Right" in the House since 1994, while the "center Right" has all but vanished from that chamber. The "center Left" has also dwindled in the House (with the gains in 2006 being almost perfectly undone in 2010). This segment of the timeline starkly represents how politics has become more polarized in the past couple of decades. I think it's neat that there's now a way to represent that visually.
Another thing that's interesting is when you see blue segments on the right and red segments on the left, indicating members of Congress who are members of "Right"- or "Left"-leaning parties, but have a voting record going against their party. There are very few points on the graphic that indicate any members of this description who aren't centrists.
Have you spotted any other interesting trends? I could do this all day.