Do you provide any documentation for playtesters to fill out before, during or after sessions, and what sort of questions do you ask? It might be helpful to have a standardised system for other developers to use. To get the ball rolling I would say initially, encouraging verboisty:
Before:- Why are you interested in this game
- What are your expectations
After:- What was your favourite thing about the game
- What did you dislike the most about the game
- If you could change one thing, what would it be
- What specific problems did you notice
- How would you fix these problems
- How would you rate the following, from one to five:
- speed
- enjoyment
- emulation
- other notes
Anyone have a copy of an existing playtester questionnaire?