Aroma is less developed in very light roasts, peaks in intensity in medium to medium-dark roasts, and falls off in very dark roasts. Complexity - Another obvious yet useful term. A complex coffee allows certain strong sensations such as acidity and sweetness to coexist. It presents a wide range of sensation, and often doesn't reveal itself immediately and definitively. Complexity is undoubtedly at its peak in the middle ranges of roast style, from medium through the moderately dark to dark roasts used for espresso.
Most blends aim to increase complexity.
Depth - Depth describes the resonance or sensual power behind the sensations that drive the taste of the coffee. It is a tricky and subjective term, but it tries to get at the way certain coffees open up and support their sensations with a sort of ringing, echoing power, whereas others simply present themselves to the palate and then stand pat or even fade. Balance - Describing coffees in which the acidity is strong but not overwhelming, the body substantial, and no taste idiosyncrasy dominates. Once you identify this taste syndrome you'll know it forever. But I'm a romantic.