Play value, diverse movement and sensory stimuli, and the guiding principle: not everything for everyone, but something for everyone. 
A good playground is characterized by high play value: diverse opportunities for movement, sensory experiences, and discovery; varied levels of difficulty; spaces for interaction; and strong design quality. The goal of high-quality planning is to address different abilities, age groups, and stages of development—without resorting to special or segregated solutions. Quality criteria, planning standards, and economic considerations are all taken into account. 
The key principle: not everything for everyone—but something for everyone.