Originality - No game can ever be truly perfect if it copies something else to be complete
Storyline - Mindless killing and fetch quests make not a legendary game
Gameplay - The main point, what is a game without the gameplay
Atmosphere (which includes Immersion) - The difference between WoW and Runes of Magic, if you feel like the areas you are in are amazing and the things you are doing are awesome then you are having fun
Length - It can't be perfect if it is too short (or possibly too long)
It doesn't exist and likely won't for a long long time.
Storyline - Mindless killing and fetch quests make not a legendary game
Gameplay - The main point, what is a game without the gameplay
Atmosphere (which includes Immersion) - The difference between WoW and Runes of Magic, if you feel like the areas you are in are amazing and the things you are doing are awesome then you are having fun
Length - It can't be perfect if it is too short (or possibly too long)
It doesn't exist and likely won't for a long long time.