It is a mixture of a Canadian whisky base with cinnamon flavoring and sweeteners, and is bottled at 33% alcohol by volume (66 U.S. proof). The product was developed in Canada by Seagram in the mid-1980s as a flavour of Dr. McGillicuddy's.
It's certainly very cinnamony, and it's not too sweet, which is a plus. A very popular shot drink on the other side of the pond, Fireball was awarded 87 points from the Beverage Testing Institute, and a Silver Medal from the International Review of Spirits.