Some of that funky flavor comes from the fact that lamb  contains a significant percentage of unsaturated fat—much more than, say, beef or pork. When this unsaturated fat oxidizes, such as when the lamb cooks, or when a sheep ages, the gamey flavor becomes more pronounced. (That’s why lamb is less gamey than mutton, which comes from older sheep.) The trick to controlling it is to use the very freshest lamb and cook it with antioxidant-rich spices, herbs, and flavorings—think mustard, rosemary, and balsamic vinegar. The antioxidants in those ingredients work to slow oxidation down, giving your feast a subtler, more crowd-pleasing flavor.
This works both ways, of course. If you prefer a more pronounced gamey flavor, cook your lamb sans antioxidant-rich trappings.