Hi Eilif.
I think it important to focus on GAME play.
If you first define the type of game you want to end up with, you can make sure the rules are the most suitable , arriving at well defined elegant and intuitive rules set.
Eg
There is a clear divide between ancient and modern land warfare.(Pre WWI and Post WWI)
In Ancient warfare a large body of troops in massed ranks is a scary sight,the same body of troops in massed ranks is just a target rich environment in modern warfare!
Also the number of elements under each players control is an important factor in determining the level of detailed interaction.
Rule of thumb,
Less than 3 , hyper detailed.
Less than a half dozen, very detailed.
Less than a dozen , detailed,
Over 2 dozen , limited detail.
Over 4 dozen , very simple.
Eg if the rules focus on individual models and the game has up to 150 models a side the interaction HAS to be made very simple to allow fast game play.
However,if models are grouped into units , and the game focuses on UNIT interactions , and each player has less than a dozen units ,This allows far more complexity in the interactions.
Anyone can get creative on the background , to up the cool factor.As asthetics are purley subjective.
But to arrive at an enjoyable and playable game , its important to be objective about the functionality of the game mechanics.
If the elements of the game interact as the players expect the rule set is intuitive.(Blod Bowl is a prime example.)
If the elements of the game do not interact as the players expect , the rule set is counter intuiitive.(
40k is a prime of this.)
What sort of rule set are you thinking of writing?