Choose a complex visualization from the web that you think would be interesting to discuss in terms of design principles (e.g. use of pre-attentive attributes and Gestalt principles), as well as evaluate (e.g. data density, data-ink ratio, lie factor).
Newspaper websites often have example visualizations you could choose from. You can also find something from the many data visualization blogs on the web. Here are a couple starting points:
All you need to submit is a link to the visualization, but be prepared to introduce and discuss your choice in class!