One of the things we did to ensure that the game's message comes across is to run people through a questionnaire after playtests or on expos. It's been pretty useful in helping to decide which side of the game's dilemma we need to push further.
(FYI, one of the objectives of the game is to make the two major choices as ambiguous as possible)
Open-ended questions are particularly interesting, because they let the players communicate in their own words how they interpret the game. It's very exciting when they mention keywords that we used in the experience goal!
Although, sure, people might be less willing to type stuff out than to tick boxes. We tried to use these questions sparingly, too.
Another thing we tried is to put two polarly opposite Likert scale (agree - disagree) questions one after another, then we use that to gauge whether the "tug" for one side is stronger than the other.
I'd like to show which questions they are but thought better since you, reading this, might run across the questionnaire in the future ;)