A well cut or faceted diamond, regardless of its shape, scintillates with fire and light -- offering the greatest brilliance and value.
While nature determines a diamond's clarity, carat weight and color, the hand of a master craftsman is necessary to release it's fire, sparkle and beauty. When a diamond is cut to good proportions (1), light will reflect from one mirror-like facet to another and disperse through the top of the stone, resulting in a display of brilliance and fire.
Diamonds that are cut too deep (2) or too shallow (3) lose light that spills through the side or bottom. As a result, poorly cut stones will be less brilliant and beautiful -- and certainly less valuable -- than well cut diamonds higher on the diamond quality scale.