The quality of being pleasant to look at or attractive.
Sightliness is a good thing because it means something looks nice or pretty.
Examples:
The sightliness of the flowers made her smile.
The sightliness of the sunset was breathtaking.
She admired the sightliness of the painting on the wall.
The sightliness of the puppy made everyone happy.
The sightliness of the mountain was so amazing, it took my breath away.
The sightliness of the garden was like a beautiful dream.