Quick answer: Post-release bug reports surface what testing missed. A targeted survey 2 weeks after release captures qualitative data beyond bug reports.
Bug reports are the obvious; surveys capture the rest.
2-week timing
Players have had time to play; not yet abandoned.
Targeted questions
'Did you experience X bug? How did it feel?' Specific; actionable.
Open ended for unknowns
'What else was wrong?' Catches the bugs you didn't ask about.
Incentivize participation
Small in-game reward for survey completion. Response rate triples.
“Surveys complement reports. Different question; different signal.”
After every major release, the survey is the qualitative metric. Plan; analyze; act.