I think the trick is to build different factions, and different strategies, so that the same approach doesn't work best for every faction. Heroes of Might & Magicwas a great gameplay system, but you were almost NEVER rewarded for focusing on creating lots of small units before moving on to the larger units.
Dominions did a much better job of balancing this across different factions, but they used very tightly scripted units with very specific abilities.
I hope the Elemental designers give us different paths to success, even for military approaches, as opposed to relying on the "uberstack" or "uberunit" methodology that underlies end-game strategy for most 4x games.
On the other hand, I also hope they make us evaluate trade-offs in our units, so any force I have will have certain weaknesses, and every decision to feature certain units means I sacrifice another path. Most games give you the option of getting archers first, or getting Iron weapons first, but the trade-offs involved in those choices aren't very big, and I can usually get both without much sacrifice. I definitely enjoy 4x games where I have to manage around certain weaknesses in my army, even in the late mid-game and beyond.
