Cameras with more dynamic range allow you to take photos with dramatic differences in highlight and shadow areas while retaining detail in both.
Think of a brilliant sunset on a rocky beach: Bright sunset in the background, with dark rocks in the foreground. High dynamic range means more of the extremes will be faithfully reproduced.
Dynamic range test data courtesy of DxO Mark.645D test data on DxO Mark 5D test data on DxO Mark
Very high-resolution 40-megapixel sensor; Plentiful controls with great placement; Excellent optical viewfinder; Dual SDHC card slots; Infrared remote sensors front and back.
High price tag; Aliasing artifacts; Produces ~70MB RAW files.