I've been having a fairly in-depth conversation among my G+ game design circle that's got me thinking about some of my instincts. In this case, I am making a casual tactical game, and rejecting or accepting various suggested improvements.
One of the things which arises fairly frequently is that I reject something that sounds reasonable. For example, because this game features retiring characters when they reach a certain level, you'll have characters in your roster that are all across the level spectrum. A level 30 knight and a level 3 pistolier.
To make it so these characters work together well, there are two basic options: a variety of techniques which allow characters to work effectively together even with low-level characters, or a mentoring system where the weaker character is artificially improved while within a few tiles of the higher level character.
Of these, I choice the mentoring system. I did this not because it had the most depth, but because it had the highest depth to headspace ratio.
What I mean by that is that it's very easy to remember "weak character within 2 tiles of strong character", and the resulting dynamics are quite interesting.
On the other hand, even though the tactical options may be even deeper using work-together abilities, they require a lot more memory. Now the player has to remember "strong knight A can click on weak knight B to enhance stat C if within D tiles", and "strong pistolier E can stand near weak knight B to automatically fire on enemy C if they attack using ranged weapons..."
In a casual game, you have to keep the headspace as low as possible, because people will only play it for short amounts of time and won't be able to track so many highly varied pieces. Because of this, I've cut a lot of complexity out of the game. The idea is to keep the core play tactically deep but not using up much headspace: two players who have never met should be able to simply swap cell phones and play each other's battle scenario from the midpoint and immediately understand most of how the team operates together. No difficult-to-grasp swarms of details like you get in Disgaea or Civilization.
"Deep play, not complex play." That's my motto here.