It is good when a game gives you that good feeling which is always attached to it. This feeling can easily be recognised and usually makes you remember what it was like when you got that feeling. This is usually caused by the atmosphere of the game or if you can connect to it. Otherwise it can be created by where you were playing, who you were playing with or just that its was a good time. It does not necessarily have to be perfect or the best graphics but it must be a game in which you feel like you are in the game or you are the character or whatever. Other than being some person sitting in front of a screen with moving images on the screen which you are controlling.