Type aficionado Tim Brown has written a great piece about how to make typographic enhancements with the OpenType features of a web font. These additions can be subtle, such as ligatures and small caps, but other tools such as kerning or contextual alternates can often have a big impact on the overall reading experience:

More than fancy swashes and superfluous ligatures, OpenType features are font superpowers. The best, most capable typefaces are full of sophisticated reasoning and delightful surprises