Mexican chocolate is prepared with an assortment of spices for a very distinctive and rich flavor.
Typically it's made from very dark chocolate mixed with sugar, cinnamon, and sometimes nuts. Other spices such as nutmeg and allspice may be added, as well as chilies. All this gives it a rather "grainy" texture.
It's traditionally used in Mexican dishes like mole and for making hot chocolate. This makes it easier to savor the rich and sometimes intense flavor. But, it's still very good eaten straight in bar form.