Line a 9-in. round pan with plastic wrap with ends extending over sides of pan. In a large bowl, beat cream cheese and 1/4 cup sugar until smooth. Add gelatin powder, lime peel and juice; mix well. Whisk in whipped topping and mint; pour into prepared pan.
Combine pretzels and remaining sugar and butter; sprinkle over gelatin mixture. Cover dessert with ends of plastic wrap; gently press crumb mixture into filling. Freeze for 3 hours or until firm.
To serve, open plastic wrap and invert onto serving plate. Remove pan and plastic wrap. Let stand at room temperature for 15 minutes before cutting into wedges.