Engagement is the most misunderstood and complex part of game analytics. The reason for this is that engagement is about fun and fun is something very difficult to infer. Average session length (measured in short units of time) and average session frequency (measured in a number of daily sessions per user) are often the metrics used to measure engagement. If we think about retention on a user count basis it is easy to see engagement as a session count and/or length basis. After all, the frequency at which players return and the amount of time they spend in the game should be good indicators of this, right?
As I see it, the difference between retention and engagement is not a matter of differentiating users from sessions. Retention is about returning to the game. Engagement is about interacting with it meaningfully. Sessions alone won’t tell you if players are having fun. Let me tell you a true story that will illustrate it perfectly. Although the story is a true one, data are illustrative.