Here are qualities that are usually NOT listed in a laptop's spec sheet:
-Build quality
-Display quality (contrast ratio, color accuracy, color gamut, viewing angle)
-Speaker quality
-Keyboard and touchpad ergonomics/quality
-Customer support
-Model specific advantages
Examples of model specific advantages:
-Hybrid graphics
-Dual battery slot
-Extra toughness
-Cell data connectivity
Here are specs that are usually listed, yet are sometimes overlooked in several ways (underestimated, miscalculated, etc):
-Dimensions
-Weight
-Battery life
-Connectivity ports
This list is by no means exhaustive.