This interesting video by the guys at ChefSteps explains in detail the process of making the perfect espresso and what happens inside the espresso machine that gives the drink such a creamy and unique taste.
Espresso is the best way to taste coffee. It speaks for itself, and the flavor is so complex and dense, and there are so many notes you can pick up. If it tastes good, then it is good, but making good espresso consistently is hard work. Preparing espresso at home is my favorite ritual. When I hand my wife a cup and saucer, and she tastes the drink, and smiles at me and says "it's good", that's when I feel like I've achieved something worthwhile.
If I'm going to a coffee shop, I tend to judge them based on their espresso, particularly with a cappuccino.