The terrain change I both like and dislike. On the one hand, in its current state it is absolutely worthless, convoluted and confusing and changing it to one terrain per province would solve it. However, I feel that there was another easier way that would currently solve nearly all of the problems of first players not knowing about it, don't know how it works if they do know about it, and if they do know it is extremely minimal or the information being misleading.
My preferred change would be that instead of "percentages" (it's in quotation marks because it's not accurately represented currently) of chance of a terrain to be picked in battle (e.g 20% grasslands, 60% hills ....) it would be displayed as maneuver score from the point of view of the defender ranging from positive six to negative six, taking into account both attacker and defending leaders maneuver. This would make it easy to see when you mouse of the terrain, make it very understandable and easy to calculate, not devalue maneuver as a stat and play into strategic thinking and rewarding awareness of the warfare and not lose an aspect of game play that could be great. This would be an simple example below:
Mountain : +5, +6
Hills: +2, +3, +4
Grasslands: -6 to +1