Chowhounds have some great alternatives to the over-the-top sweetness of sweet potatoes with marshmallows or streusel. foodslut keeps it extra-simple, parboiling them, then roasting with a bit of butter and salt. itryalot makes a simple casserole by first roasting sweet potatoes skin-on, then scooping out the insides and mixing with an egg and heated milk in which she’s steeped garlic cloves, then baking in a casserole dish at 375°F until bubbly.
greenstate cubes them and tosses them with olive oil, salt, pepper, cinnamon, and cloves and roasts with maple syrup or brown sugar. btnfood likes this sweet potato casserole with ginger (link leads to a PDF file) and says “the slightly bitter molasses and spicy sharpness of the fresh ginger and cayenne really enhance the sweet potatoes without drowning them in sugar.”