The retrospective is the most powerful of the agile meetings. If you are able to keep this interesting you stand a much better chance of successfully implementing agile.  
Gamestorming is an easy-to-comprehend-and-apply guidebook to a new method of brainstorming; a world in which we use the basic foundations of games (yes, games) to think through challenging or sophisticated problems. 
You'll see that using Gamestorming in your retrospectives makes them even more powerful. Session outline:

• Explanation on the importance of retrospectives
• Explanation about Gamestorming and some techniques
• Do the Speedboat exercise 
• Short "retro" to look back at the meeting to identity "take-aways" for people