(Photo: AFP/Getty Images) The stock market is having a quiet year in 2015. The famed S&P 500 index is up a meager 2.3% since the New Year, and the Dow Jones Industrials index has lost 0.4%. But there are always exceptions to the rule. We asked a panel of Motley Fool contributors to outline the five biggest surprises they've seen in 2015, and this is what they came up with. Here, you'll find a few long-running turnaround stories such as video-game designerElectronic Arts (NASDAQ:EA) and casino operator Isle of Capri Casinos (NASDAQ:ISLE). Digital entertainment veteran Netflix (NASDAQ:NFLX), meanwhile, is going from strength to strength, and former bargain-bin shoe designer Skechers USA (NYSE:SKX) has become a powerhouse footwear brand in its own right. And what the heck is Natural Health Trends(NASDAQ:NHTC), other than a market-crushing titan in 2015? You'll soon find out. These stocks have gained between 54% and 152% so far this year -- and that includes retreats from much loftier yearly highs in some cases. Dig into these juicy stock stories right here: Brian Stoffel (Netflix): Let's consider where Netflix stood when it entered 2015. Although the company's stock had fallen 25% in the last three months of 2014, it still traded for a hefty valuation. Shares were valued at 90 times trailing earnings, and Netflix hadn't produced positive free cash flow during the year. The company had just announced ambitious plans to expand to nearly every country on the map, and warned that it would take a while before its investments truly paid off. Since then, the stock has more than doubled -- up an amazing 125% in just seven months' time. While it's still a mighty expensive holding -- now over 300 times trailing earnings -- the company's success at growing its subscriber base truly stands out. Total global streaming subscriptions rose a whopping 30% to 65.5 million from the second quarter of 2014 to the same time frame this year. The biggest gains came outside the U.S. One year ago, there were 13.8 million international subscribers to Netflix services. That number has jumped almost 70% since then to 23.25 million. That kind of growth shows just how popular Netflix is with an international audience, and why the stock has done so well over such a short time frame. Rich Duprey (Isle of Capri Casinos): For a casino operator that once seemed to be on its deathbed as the island gambling oasis of Macau off mainland China attracted betting and investment dollars, Isle of Capri Casinos has to be one of the most surprising turnaround stories -- not only of this year, but of the past few years. The casino operator's recovery began last year, but has accelerated in earnest in 2015, with shares more than doubling since the start of the year. Isle of Capri Casinos owns or operates 15 casinos in seven states, and strong performance has fueled its drive higher, with revenue and earnings topping analyst... More