Aside from the dark roasted espresso-style flavor, the main attraction of Bustelo is the fact that it's cheap. As in, really cheap. The 10 oz. can in the photo ran me about $3. In fact, it's a good thing to just grab and keep in the pantry for emergencies, or when you've got a recipe that calls for a few ounces of espresso and you don't have a steam pressure machine.
How is it? On its own, the coffee is strong, bitter, black, almost burnt. I crave and adore bitter flavors, so obviously I'm a fan, but I wouldn't recommend drinking several large cups of it first thing in the morning. It's really meant to be enjoyed in small dozes, or as café con leche in a one-to-one ratio with milk, plus sugar to taste. The sweetness of the sugar and the creamy/savory milk balance out the powerful flavors, but do not completely mask them as would happen with plain coffee. This concept is why Starbucks has historically been so successful: not selling coffee, but selling
One bit of advice: the fine grind of Bustelo can be a little muddy if you're using a French press. If this bothers you, just give it a quick strain through a filter, or avoid pouring the last dregs from the carafe. Otherwise, cowboy up and drink the stray grounds like a real man.