Not to simple, not to complex, with a uniquely strategic play style, and a map editor for single/VS/co-op possibilities.
From soldiers to tanks, planes, choppers, subs, battleships, flame throwing vehicles, etc this turn based strategy game has it's own unique feel that nails what a casual TBStrategy game should be. Capture and utilize towns to produce income, and capture production buildings to purchase new units. As towns mature they generate more income. Use hills, mountains and trees to tactical advantage, take calculated risks and fight across the board to capture the enemy's main base. Bring a few medics along to heal your troops. Use jets as a quick mobile strike force, buy some long range weapons, but be careful with the expensive stuff, you can afford only so many toys.
And what really makes the game so much fun is the included level editor which can be used to create single player, versus, and co-op scenarios. This really makes the game a classic with unlimited replay potential. Although it's a budget game, it's one of the best games I've played, and has provided more than a few hours of play time, to put it lightly.