There are 2 methods you can enable or disable the Post-Game Summary; one through the application and another through the website:
You can visit your Notifications link by going here: http://raptr.com/account/notifications
Once there, you can enable/disable the checkbox for "You play a game or earn achievements"
You must first enter into your Preferences and go to the "Alerts & Sounds" tab
After that, you will want to enable/disable the option for "Show me a summary after I finish playing a game"