One thing that keeps me going on strategy games is the personal characters. Instead of a cascade of five-pixel high soldiers I prefer fewer but more personalized units.

They could have features like name, rang, morale etc. After each mission they achieve promotion or other increment depending on their performances in battle. Someone mentioned commanders and that´s a good start.

Perhaps it´s too complicated to give attributes to each unit, maybe a group of units is more realistic. (Haven´t tried out this kind of games on my own yet)

I think it´s much more fun to "get to know" the soldiers or vehicle-crews. Then you really wants them to survive and get better. You don´t just send them on suicide missions because it´s fun.

The ideas about water, wheather and day-night cycles seem great!

Happy Programming!