One of the most fascinating aspects of XCOM 2: War of the Chosen is the Enemy Unknown's tactics. The E Unknown is a cunning foe that uses a range of strategies to defeat the player. It will often:

And if you don’t want to mod? Buy XCOM: Enemy Unknown - Complete Edition for $10 on a sale. It remains one of the greatest turn-based tactics games ever made. Just remember: That’s XCOM, Baby.

Kelly watched as a Viper slithered from the rooftops, its long tongue flicking out to ensnare Miller. With a roar, she vaulted over her cover, her machete gleaming under the city lights. She sliced through the alien’s scales just as the ADVENT reinforcements arrived—a drop pod screaming down from the sky.

"Lock and load, Strike Team," Bradford’s voice crackled through the comms. "We’re going in quiet, but we won't be staying that way."

Bradford argues for a suicide strike on Brasilia. Dr. Tygan discovers the truth: the Commander’s mind is still partially linked to the Elder network. If the Commander severs the link, they’ll lose their strategic genius forever—but the Elders will be blinded.

This is the core of your search. You want the XCOM 2 engine (better graphics, mod support, smoother UI) but the Enemy Unknown feel (starting from scratch, defending Earth, no timers). Here is the recipe.