Preheat oven to 350°.
Mix the graham cracker crumbs, melted butter and sugar together until well combined. Press into the bottom of a 9" springform pan.
Blend the cream cheese, sguar and vanilla with an electric mixer until well blended and smooth. Add eggs, continue to mix for 2-3 minutes until well blended. Stir in half of the chopped Hershey bars and then pour into crust.
Sprinkle with remaining Hershey bars, marshmallows and coarsely chopped graham crackers.
Bake at 350° for about 60 minutes, or until center is completely set. You can use a toothpick to check-some of the cheesecake filling may stick to it a little bit, but you'll be able to tell if it's runny or set.
Keep an eye on the cheesecake for the last 10-15 minutes of baking - if the marshmallows start to brown too much before the center is set, you can loosely cover the cheesecake with foil for the last part of baking. I like the marshmallows pretty toasty, so I don't usually find that necessary, but if you don't want them quite so brown, the foil will help.
Let cool for about 30-40 minutes on the counter and then refrigerate at least 3 hours (preferably overnight) before slicing and serving.