I think adding uncertainty is definitely a plus. Something like infantry units not being as effective as they are in a certain terrain. Infantry is just too good at the moment while archers are somewhat unreliable.
I definitely like the idea of different kinds of terrain modifiers. Various versions of that have been suggested over the years, to mostly positive reception. The trouble is implementing it in a clean and balanced way, that has enough effect to be meaningful, but not so much as to completely throw the game out of whack.
