response to Z: Well, it isn't required to play both games, I can't check that, but it won't be as good as if you've played both, due to the fact that watching some let's plays won't be as good as playing certain game on your own. About sharing the results, we will see.
response to mushroom patch: I've tried to pick the most similar games which I could think of, probably the worst pair in this study is Shadowrun vs Fallout 2 comparison, due to the fact that there's difference of 15 years between both releases. If there was any better candidate it's too late to change it.
Also I'll probably do more questionnaires, this time without comparison (only kickstarted games) for people who couldn't play both (they're majority after all), but it doesn't mean that these are worthless, they will be just as addition to the whole study. In case someone wonder, why I was doing comparison and now I want to change it. The teacher who helps me doing the study isn't interested in gaming, and he proposed to do comparison, I've contacted him lately and now he accepted the change to the research. Now all I have to do is to make new questionnaires that can provide data required to create good conclusions. I'll update the original post soon.
PS if I made any mistakes, I apologize, english isn't my native language.