Dumbed down from SCFA, and not nearly as deep, or as fun, but still worth a play if you can get it on sale. Definitely buy Planetary Annihilation first.

Though it is aging, Warband blends intense, ferocious, and immersive combat with complex and enjoyable strategy elements. A genre-defining game.

A heartwrenching game that requires more strategy and brainpower than one might, at first, think.

Several of us have thousands of hours in XCOM. Enough said.

War Thunder offers immersive gameplay in a range from arcade style to full simulation, and is only getting better. Can't ask for more for $0.

DOTA 2, like all MOBAs, has some elements of the twitch-reflex game, but the item system and variety of gameplay makes DOTA 2 stand out.

Supreme Commander: Forged Alliance adds even more depth to the franchise with new tech, a new race, and more maps.

Supreme Commander is the ultimate grand strategy game, the predecessor to SCFA and, more distantly, Planetary Annihilation.