I'd like to see terrain be somewhat more interesting.
Suggestion 1: More inherent differences between terrain types, e.g. movement penalties to various unit types (and nullification of these under certain circumstances, e.g. bears in woods or lizards in swamps), more varied combat boni und penalties (and variations on these with certain types, also types of training available to units), more variation in tactical battles (e.g. danger of fire in woods, difficulty with fire in swamps, chance of getting siege units stuck in swamps, etc...)
Suggestion 2: More strategic advantages and disadvantages. In other classic games (e.g. Civilization or Dominions), terrain mattered; here, it doesn't seem to. Make certain terrain types offer more inherent materials but less advantages from prestige, or have a higher rate of bad events, etc, while others should give inherent food boni while being meager with materials.
As it is, the terrain differences feel bland, uniform and somehow abstract.