For good overall skiing, temperatures in the 20s or low 30s F are considered ideal. The snow won't get too heavy or slushy, yet it's not so cold that you will get chilled on the lift.
There's no feeling quite like floating down a slope in a foot of untracked powder. Even when you fall, the snow is soft. Good powder skiing, once you get used to the technique, is like hero snow. Six inches to a foot is ideal; more than that can make lower angle slopes difficult to ski.
The light can greatly affect how enjoyable skiing is. Blue skies are ideal, and skiing in a snowstorm can also be fun. When the light goes flat, generally under gray skies, it can make it hard to make out undulations in the snow surface and make skiing unpleasant.
Packed powder is a ubiquitous term that can mean a variety of things depending on where you are skiing. In the east, it can refer to a hard surface just under ice. In the Rockies, packed powder can be softer and fun to ski.
After a long winter of skiing in the cold, when the weather starts to warm, it can produce a cycle that creates corn snow. Corn snow has a velvety texture and is a joy to ski in temps that are in the low 40s to low 50s F. When spring skiing, it is a good idea to go later in the morning so the snow has time to unfreeze.