ggplot2 is absolutely excellent, with much aesthetically appealing default features compared to the built-in graphic system. Moreover, the adoption of the intuitive grammar structure makes things easier and more intuitive. I am very happy with it. I personally thank the authors for his great contribution.
A few small problems:
1. the graph engine is a bit slow, even for some simple graphs. By the way,
2. I don't know how to put Greek letters into annotations, though Greek letters work in the coordinate labels via expression( ).
3. geom_density( ) generated an ugly horizontal line at y=0. It should not be there.