This version of Superman had romantic feelings for Lois Lane that he was largely unaware of. However, when she was killed in a car bombing staged by Intergang, Superman was grief-stricken and proceeded to rethink his priorities. He soon came to perceive a war on crime, believing that showing a positive example for the populace wasn't enough after all. Realizing that he would need to work on a much larger scale in order to win the "war", he approached Lex Luthor and forged an alliance with him, as Luthor had the organization and technology that Superman needed. Together, they took over Metropolis and eliminated crime, but they also eliminated freedom. S.T.A.R Labs and the Daily Planet were among the businesses closed due to the takeover. This version of Superman is gruff and grim, having little patience or understanding for wrongdoers and dealing with them in a rough manner. Superman also never learned that Luthor had secretly been imprisoning everyone who didn't go along with the program, even to the point where he had the power to declare anyone an unfit parent and have their children remanded to an orphanage owned and operated by Lexcorp.
Superman would eventually learn the truth when he encountered the Lois Lane from (the regular) Superman's universe. All was revealed when he saved Lois from the security forces and tended to her injuries in his penthouse apartment. Upon hearing how this version of Superman had come to work with Luthor, Lois expressed her disgust as well as anger at finding out this version of Superman had never approached his version of Lois and discussed their relationship. Lois had already met Jimmy Olsen. Jimmy was arrested for his resistance activities and Lois witnessed the truths behind the repressive regime.
Until meeting the alternate Lois Lane, Superman believed that Lex wouldn't try anything devious behind his back for fear of his reaction, a belief that was shattered when he learned that Luthor tried to kill this Lois Lane. She showed him a holding cell located in the tower in which Superman resided since the takeover. The impact really hit home when Superman was jeered and pelted with brickbats from the captured rebels.
It was then that Superman stormed into Luthor's office and told him of his problems with his job performance. Lex responded with a "gift" from the people of Metropolis: the Kryptonite that the resistance had taken earlier. He planned to 'prove' that he tried to restrain Superman's wrath and was forced to kill him to protect the people. Superman had beaten Luthor to the punch, as the rebels were brought into Luthor's office, with Superman saying he had gained their trust (albeit probationary) by hearing out their grievances. Luthor fled, followed by Superman. Luthor was killed when he crashed into his side of the monument dedicated to the union of Superman and Lex Luthor.
At the ruins of S.T.A.R. Labs, Superman promised the alternate Lois that he'd restore Metropolis to what it used to be. Then the portal Lois came through opened and Superman saw his counterpart trying to bring Lois back. He and the alternate Lois exchanged a kiss and took their bittersweet leave of each other. The blue-suited Superman took one last look at his black-suited counterpart and left.