There are two ways to drink whisky. (Ok, besides pour in glass, pour in mouth and repeat.)
You drink to enjoy whisky and you drink to explore whisky. When you want to enjoy whisky, then anything that holds liquid will work: A tumbler, a flask, a cocktail glass, a (clean) boot... whatever.
When you want to explore whisky... to dive deeper into the dram... to discover its notes and subtleties, then you need a glass designed for that purpose. Look for a tulip shaped glass - one that is tapered towards the top to funnel all those aromas up. The Glen Cairn glass is an extremely popular choice as it is used at many tastings and whisky bars. The others are variations of that design, each, offer their take on the nosing and tasting experience.
Cheers. Slainte.
