"This is a subtle one. I can see why some find it bland. First, half the recipe. It makes a massive amount of very heavy, dense food. Second, use game. I've made this twice, and the venison brings it from ho hum to fantastic. Third, use the right amount of porcini. Those little packets in the supermarket are just half an ounce - you need 3X that for the full recipe. That's probably a lot more than most of us want to spend on a working class hero dish like shepherd's pie, but the flavors do not come together here without it. Finally - don't skimp on the parsnips in the potatoes. The parsnip-potato mash is fantastic, and you need it on the fork with the base for the flavors in the latter to shine. Do all this, and you won't be disappointed.