Novo Nordisk's stock may look expensive today, but that may not be the case in even a year or two.Danish pharmaceutical company Novo Nordisk (NVO -0.86%) has established itself as one of the top healthcare stocks in the world with a market cap hovering around $600 billion. Long-term investors earned fantastic returns; in just five years, the share prices of Novo Nordisk are up over 450%. But what about investors who buy the stock today?Does Novo Nordisk have the potential to keep generating great returns? A ...