Google’s HEART framework for UI metrics

In order to pick the proper feature-level metrics, exploring
Google’s HEART framework for UI metrics may be a good starting
point:

H – Happiness Metrics (like user satisfaction scores)
E – Engagement Metrics (like average visits or uses per user)
A – Adoption Metrics (like new users)
R – Retention Metrics (like churn)
T – Task Success Metrics (like form error rates)