A well made pie is a thing of beauty. The pastry really does enhance the experience like with apple pie. I rarely eat them these days because the pastry makes it extremely calorific. I eat stew of course, just not pastry as a general rule.
Most of the shop ones will be shit. The same as the so-called Cornish pasties. They aren't difficult to make but they all skimp on one of the following: good quality fat in the pastry, meat content, viscosity of gravy and herbs/spices. Stay away from tin pies like Fray Bentos at all costs.
Pies taste like a thick stew in a pastry crust. The top will tend to be more crispy than the bottom, which will be of a wetter, more stodgy consistency. Many people like the contrast between the top and the bottom.
The beef/chicken pies tend to be more of a stew than the pork/game ones. The pork/game ones tend to be more densely packed and solid with a jelly that sets in a layer between the pie crust and the filling (for preservation).
Good sides to have depends on the pie. Beef goes with peas, seared tendersteam broccoli, carrots, mash, gravy (not ketchup/HP sauce!). Piccalilli and vinegary condiments like pickled eggs/walnuts go with pork pies. Redcurrant jelly with game. Trust your taste.
Beef/steak & kidney pies tend to be eaten at home as the main part of a meal or hand-held in a football stadium. The hand-held ones tend to be more viscous. The idea is that you need enough gravy so you don't have a dry eating experience but not so runny that it makes a mess when you try to eat it. Nowadays they give you a plastic tray and pour gravy on top of the pie as well. This makes it extra moist but you lose the flakiness of the top as it becomes more soggy. Some people like that.
Pork pies tend to be eaten cold at picnics. You cut a slice (not the whole pie in other words) and have it with whatever else you are having. Things like quiche, scotch eggs, small sandwiches, cold cuts, cheese like cheddar, jam tarts, fairy cakes etc.