Despite all these tasty ingredients, the potatoes can sometimes be bland. They have a natural ability to soak up lots of seasoning, so try seasoning more than you usually would.
Instead of seasoning just the sauce and tossing it with the potatoes, try salting and peppering each layer of potato slices, one after the other, and then pour the sauce on top.
This creates thoroughly seasoned potatoes so not a single bite of the casserole is bland. For even more flavor, try adding herbs, spices, different cheeses, or broth to the sauce.