Shares of Amazon.com ( AMZN) are getting crushed. But considering the stock's run this year and the rich valuation it commands, shareholders can't really complain. Shares of the online retail giant were off nearly 15% to $86 in recent trading on Wednesday, a day after the company reported third-quarter earnings. While Amazon edged ahead of Wall Street's top- and bottom-line expectations, the company couldn't hold up against increasingly heady expectations. Still, shares of Amazon are up almost 120% year to date, making it the best-performing large-cap stock in the Internet sector by a wide margin. Runner-up Google ( GOOG) has climbed "only" 45% this year. Amazon also remains the most richly valued. Its shares trade at about 55 times forward earnings, and the stock commands a price-to-earnings-to-growth ratio of almost 4. Google trades at about 32 times forward earnings and has a PEG ratio of 1.3. That means investors should hesitate before viewing the current selloff as a buying opportunity. Wednesday's downturn may be overdone given the broader market's decline -- the Nasdaq was off 2.2% in afternoon trading. And Amazon may move higher as part of a broader recovery. Despite the company's impressive progress, it's difficult to make the case for the stock at these levels.