[Suicide Junkie]

You do need some minimum amount of complexity (to get beyond tic-tac-toe and rock-paper-scissors), but simple can make for great depth.

Consider CBmod, for example. As far as the datafiles go, it is quite simple. At the same time it has a lot of strategic depth due to the flexibility and balance (if I do say so myself).

It seems to me that too many people try to add complexity with an iron fist and choke off depth by accident as a side effect.