The roasting section actually has a few hidden gems. The first "pop" (called the first crack in roasting lingo) occurs slightly after the green bean begins to brown from carmelization and the moisture trapped inside rapidly expands via evaporation cracking the bean. After the first crack is known as a City Roast and is lighter, more woody and fruity tasting than the darker roasts.

The second crack occurs shortly after the first one at the end of the City Roast range as the cellulose matrices that form the coffee bean themselves begin to break down from the heat damage. At exactly the start of the second crack the beans are called Vienna roasted and begin to have darker, richer flavors. These coffees are where you hear about honey and chocolate flavors.

As you keep going the beans will continue to crack as they begin to literally degrade to ash. Further carbonization begins to take over the flavor alongside the aromatic oils which seep out of the now lipid-hostile inner bean environment. These form the oily-looking French roasts which are known for strong flavors, intense bodies, and bitterness.

If you do start to buy fresh coffee, play with the roasts. A single bean from a single place in the world has a wide spectrum of flavors depending on how long it's been roasted.

Notes: http://www.sweetmarias.com/roasting-VisualGuideV2.php