In a medium bowl, combine crushed cereal, brown sugar and melted butter. Press into the bottom of an 8x11 dish. Set aside.
Using a mixer, beat cream cheese, pumpkin puree, sugar and pumpkin pie spice until smooth and well blended. Spoon in 2 ½ cups of whipped topping and gently stir to combine.
Pour mixture over cinnamon crust and spread evenly. Refrigerate at least 4 hours or until firm.
Slice into bars and serve with remaining whipped topping and sprinkle with pumpkin pie spice, if desired.