And would only add try using different types of cheese which will melt at differnt temperatures so give you a nice texture.
Also,
add some crumbled blue cheese in the pie for a tangy taste,
top with breadcrumbs for a crunchy top
- or use flavoured crisps, like a cheese and onion or if you are adding bacon to the pie, use smoky bacon crisps - crunch them up and sprinkle over the top
as an option use sliced par-boiled potatoes rather than as a mash - layer with sliced onions, make up a simple cheese sauce (white sauce and add grated cheese) pour over, top and bake to finish
add some finely sliced tomatoes to the top of the pie - looks nice and adds a nice flavour
use a tiny pinch of smoked aprika in the pie - goes really well with cheese and with potato dishes too - but only a little pinch as it can overpower the rest of the favours