My students really enjoy creating their characters and then customizing them with outfits. They like to mix and match, and take a lot of time to make their avatar look as much like them as possible.
While they would love even more customization ability with their avatar (hair, features, etc), the big one that comes up every year is skin color. Many of my students wish there were more skin color options, especially for darker colors. That could make them even more invested, as they identify with their avatar more.