Roasting coffee causes complex chemical reactions to take place within the coffee seed, and how the coffee is roasted will accentuate or diminish inherent qualities.  This is why one coffee can be roasted different ways and offer different flavor experiences.  Generally speaking, lighter roasted coffees tend to highlight the flavor and aroma attributes that make the coffee unique, and they tend to be high in sweetness, high in acidity, and thinner in body/mouthfeel. Many lighter roasted coffees are often described as being tea-like. As the coffee approaches the medium roast level, most coffees continue to become sweeter, less acidic, and increase in body, but the unique flavors and aromas start to diminish. For many coffees, the medium roast level is where all of these attributes find a sense of balance. As the coffee continues to roast darker, most coffees become less sweet, less acidic, and increase in body, and there is a tipping point where sweetness is eclipsed by bitterness and the coffee begins to lose body. The unique flavors and aromas continue to diminish and will eventually be eclipsed by roasty (eventually burnt) flavors and smokey aromas.  This is not say that one roast level is good and another is bad. Coffee just isn’t this simplistic. Taste is subjective and everyone has their own personal preferences regarding flavors, aromas, and textures. The coffee that is right for you is the coffee you enjoy.