Quality is defined as an objective or subjective experience.
Objective:
In advance you define specific properties and functionality.
If you can later on fulfill these goals or even excel them you have a good quality, if not, well...
Subjective:
If you subjective expectations are fulfilled than it's a good quality for you.
Games related you can measure the objective case by defining the properties in advance (gfx, sfx, gameplay, story, depth, ...) and subjective it's anything which pleases you.
Objective:
In advance you define specific properties and functionality.
If you can later on fulfill these goals or even excel them you have a good quality, if not, well...
Subjective:
If you subjective expectations are fulfilled than it's a good quality for you.
Games related you can measure the objective case by defining the properties in advance (gfx, sfx, gameplay, story, depth, ...) and subjective it's anything which pleases you.