Each realm has a monarch who must survive at all costs and builds the first tier construction units, who then build the next tier and so on, up to tier four. The basic first tier units are grunts and serve similar functions for all races, even though their capabilities vary vastly. For example, the Fire archers are pretty weak, while the Air archers are proficient. That doesn't mean you don't build the Fire archers at all, you just use them only when you don't have any other units to do the same job. In between, the construction tree differs wildly.
Earth has some great artillery and a complete assortment of ground units, but little else.
Finally, Water is the only race with a decent navy, and while less versatile on the ground, boasts good defensive structures, long range musketeers and bombarding dirigibles that can turn the tide of any battle. The basic design and the resulting gameplay is solid, loaded with surprises and open to different tactics. No complaints there. But the overall package has its flaws. Zhon hunters take the high ground.