Own Insights (while dreaming?):

May apply to ANY game, really.

1. Cool — Has to look cool; a certain aesthetic.? At a minimum, achieve the standards of whatever a ‘professional’ piece is. See alien hominid.
2. Internally Valid/ Consistent — The rules, the mechanic has to make sense and continues to make sense throughout the game.? Rules set out in the beginning should apply in the end; the mechanic should carry on no matter how complex those rles may get.?? See Magic the Gathering.
3. Simple –? At the outset and throughout it must be easy to understand and logical; nuances build upon nuances so that it may quickly have the appearances of getting complicated.? See that Pokemon game that Anita’s Parents love so much.
3. Deep and Rewarding — Users must be rewarded, and the game necessarily advanced, by “discovering” other aspects of the game not initially apparent, such as secret moves.? See Street Fighter II.
4. Hook — Some interesting twist, be it topical (what just happened in the ‘news’), gimmicky, or whatever, to differentiate and make it different.