Coffee is predominantly bitter, nearly as bitter as unsweetened chocolate
Welcome to the board. My point is that it's easier to find the right espresso when you know what tastes you seek. People look for two things in espresso: the right sort of bitterness, which is a question of taste; and a balanced shot, which is a question of quality.
Most espresso served in run of the mill cafes is unbalanced, and their bitterness is thoroughly unpleasant. Bitterness needs to be balanced with sweetness and optionally, some lively acidity. For poor espresso, adding sugar is absolutely necessary. This is not a disgrace in an Italian cafe serving 80 cent per shot, high percentage Robusta coffees -- they are doing the best within their budget. But it is a disgrace for a cafe that serves specialty coffee; because specialty coffee is naturally sweet enough to balance the bitterness and acidity, and they are screwing that up in the roast or shot preparation. All the roasters and coffees recommended here at HB are superb in this respect.
Once the coffee is balanced, you may still prefer some flavors to others. Lighter roasted espresso has apricot, floral, and citrus tastes on top, backed up by toasty, woody, and honey like flavors underneath. Our favorite roasters typically offer coffees like this as "Single Origin" specials. The medium roasted coffees have some berry flavors on top, with caramel and chocolate flavors underneath. The main blends of our favorite roasters typically fall in this class. A good dark roasted blend has dried fruit flavors and lemon peel twist on top; and spice, dark molasses, and peaty flavors underneath. Oddly enough, nobody here has any great dark blend tips; it seems when people get away from Starbucks, and become coffee connoisseurs, they entirely avoid darker roasts, whether good or bad. A few years back, Dallis Brothers made a blend like this called Five Points, but I don't know if it's still around.
I hope this gets you started.