What is considered a high quality whiskey?

What are the key factors that determine the quality of a whiskey? Is it the age of the whiskey, the type of grain used, the distillation process, or a combination of all these? How does the taste and aroma of a high-quality whiskey differ from a lesser quality one? Are there any specific brands or regions that are known for producing high-quality whiskey? And finally, how can one tell if a whiskey is of high quality just by looking at it or tasting it?