Is it playing like we designed it to?
Game metric is where you collect data about the game as people play it and than analyze the data to try to make the gameplay experience better. The three core steps is telemetry, archive and data mining.
Telemetry - Is the step that gathers the data from the game and send it to you.
Archive - Store the data you have collected.
Data mining - Parse it, present it and try to make sense of it.
Most players do not approve of excessive data collection that run run on the players hardware. There are some basic things that can be done to make them hate you less.
Give players a way to opt-out of all or part of the data collection.
Applying Data Mining to Extract Design Patterns from Unreal Tournament Levels - 2014
Comparison of Human and AI Bots in StarCraft with Replay Data Mining - 2013
Predicting Player Behavior in Tomb Raider: Underworld - 2010
Standard Gameplay and IAP Metrics for Mobile Games - 2010 Part 1, Part 2 and Part 3
Design Testing: The use of addiction metrics to force rapid evolution of innovative game designs - 2005