GGPlot2 is the second version of an R implementation of the Grammar of Graphics. It makes gorgeous graphs by default, but the defaults are correspondingly harder to override. The package is being actively developed, so this may change.
You want to use ggplot2 if:
- you're building a relatively simple figure and want quick, pretty results
- you don't mind thinking about graphics in a new way
- you want to do lots of visual data exploration on a relatively small data set
- you're online while you're working (the best documentation is on a website)