A shepherd's pie is extremely easy to jazz up.  Consider
these variations.

Creamy Chicken
Use ground chicken in place of beef, cream of mushroom soup and poultry seasoning or tarragon for seasonings.

Sassy Italian
Remove Italian sausage from the casing and use instead of beef.  Chopped sweet pepper could be used as the vegetable.

Mexican
Stir 1/4 to 1/2 cup hot salsa into the cooked beef and add 1/4 to 1/2 tsp. dried chilies.

Mashed Potato Stir Ins
For extra flavor stir grated cheese, chopped chives or green onions, crushed garlic or cayenne pepper into the mashed potatoes before spreading over the filling.