You got that right. I checked the missions from SC2 and AOE2 to get some ideas. SC2 solves the boring game problem by introducing new units step by step. You may have noticed units in my game do not share the same role(tank, damage dealer, healer). This was intentional.
I wanted to add story but I think it would take way too much time to draw all the CG. Actually, I'm planning to learn Blender next year to make a 3D game. Maybe I should make a game starring hand cannoneer who teams up with giantess. I'll try to include a story in my next work.