I seem to be in the extreme minority opinion that ggplot2 has facilitated the creation of millions of ugly charts. The default theming hurts my eyes. Much improvement can come from just adding + theme_bw() or + theme_minimal() as the last layer.

But it is flexible, and it's fun. I have enjoyed following other's examples of recreating chart themes mimicked from the Economist and FiveThirtyEight. I think the latter often does employ ggplot2 with heavy customization to create some nice looking visualizations.