Researchers have identified that smiling, happy Lego characters are becoming less and less common.

After studying over 3,655 figures, experts at the University of Canterbury in New Zealand and the Industrial Research Institute for Automation and Measurements in Poland found that the number of happy faces on Lego characters has fallen since the 1990s.

This has given rise to more angry and fearsom Lego facial expressions.  This change is believed to be due to the introduction of conflict-based themses in their sets, depicting scenes of war. 

Source: Agents with Faces