Cheeses usually become not only firmer but more pungent as they age, so most of the cheeses in this category pack a lot of flavor. They're often grated onto pasta dishes. Firm cheeses have a much longer shelf life than their softer counterparts.
Most blue cheeses are made with cow's milk. Cheeses made with sheep's milk, like Manchego or Pecorino, have more butterfat, which make them richer and creamier. Cheeses made with goat's milk, like Crottin de Chavignol, tend to have a tangy, earthy, and sometimes barnyard flavor.