While on the surface this game may appear simple, the way it uses it's
rock-paper-scissor mechanic adds so much to it's depth and competitive strategy.
The game has many many skirmish maps as well as a long story-based camaign.
The skirmish maps are balanced, whereas the campaign puts you in various positions that you have to work your way out of as well as easing you into the game so you can learn the units a few at a time.
There are a good variety of units, each with different strengths and weaknesses, to be used in different situations. Grunts, the standard infantry, are relatively cheap at $75. But should they come up agains a Sniper ($200) which has superior range, they can be one-shotted. Sending a Scout Tank ($100) could have the speed to get close enough to take out the Sniper, unless there's a Bazooka ($100) nearby, which could one-shot the Scout Tank.
There's such a complexity between all the units, divided into land, sea, and air; I could go on forever. Worth the $10.