Principles
These are some principles I like in game design.
Time not grind
Time not grind
Timers (i.e. those most commonly used in free-to-play titles) aren't inherently bad, the use of timers to convert players by exponentially increasing the wait time can detract from the game experience. Timers are preferable to grind as a mechanism for lengthing the players engagement with the game.
Reference material
Reference material
The game should be complicated enough that players will need to refer to reference charts or wikis.