Qualitative data is OK, but without a really strong understanding of social theory and stuff like desirability bias there's a big risk of not asking the right questions and making misinformed decisions.
One way we've found to limit this risk is by supplementing hypotheses developed through qualitative research with a quantitative approach.
So, ask users what they like/dislike about an experience to formulate an idea of what changes to your app may better the experience, BUT make sure to then TEST those changes using a rigorous method (i.e.: experimentation or A/B testing) to validate that the feedback you're hearing is not just noise...
One way we've found to limit this risk is by supplementing hypotheses developed through qualitative research with a quantitative approach.
So, ask users what they like/dislike about an experience to formulate an idea of what changes to your app may better the experience, BUT make sure to then TEST those changes using a rigorous method (i.e.: experimentation or A/B testing) to validate that the feedback you're hearing is not just noise...