In an episode of Justice League (the excellent animated series), A Better World, an alternate universe version of Superman killed Lex Luthor, just like what Oliver did in Requiem. I decided to do a little comparison.
In Justice League, that version of Lex Luthor becomes the president of the United States of America, but he is a raving lunatic who kills the Flash for reasons unknown and intends to launch a nuclear war (reminds me of Apocalypse).
Justice Lord Superman: There are at least six different ways I can stop you right now.
President Luthor: But they all involve deadly force, don't they? And you don't do that. No, you need me. You wouldn't be much of a hero without a villain, and you do love being a hero, don't you? The cheering children, the swooning women, you love it so much, it's made you my most reliable accomplice... You could've crushed me any time you wanted and It wasn't the law or the will of the people that stopped you. It was your ego. Being a hero was too important to you. You're as much responsible as I am. So go ahead, fix it somehow, put me on trial, lock me up, but I'll beat it and then we'll start the whole thing all over again.
Justice Lord Superman: I did love being a hero, but if this is where it leads, I'm done with it.
And with that, Superman kills Luthor with heat vision.
In Smallville, of course, Lex Luthor is an evil man by the time of Requiem. Yet, Lex and Oliver started off as friends as kids, only for Oliver and his gang to bully the largely isolated Lex in school (Reunion), and that is partly what makes Lex into who he is today. While Lex has committed many crimes, the prime reason for Oliver to go after Lex seems to be revenge for his parent's death...at Lionel's hands. While Lex eventually tries to kill Oliver (Requiem), Oliver is perfectly willing to kill Lex before that (Bride).
After killing Luthor, Superman's relationship with Lois Lane becomes very tense, despite the fact that she acknowledged Luthor's murderous vendetta against Superman (Solar Power and Hereafter; on a completely irrelevant note, Lex is playing with bow and arrows in the former occasion when Lois accuses him of weakening Superman). In an ironic contrast, Oliver gets to hook up with everyone's dream girl (okay, that's just my description) less than a season after killing Lex. Who chews him out on the act, goes through a divorce and had her reconciled ex-husband die in her arms to boot.
The Justice Lords discover the dimension of the Justice League, and decide to spread their rule. Lord Superman stops Doomsday's rampage in Metropolis, and the crowd actually cheers for them. Even when this universe's Luthor breaks out of prison (again), the Lords are reluctant to do the same thing to this version (he isn't an immediate threat this time...or so they think).
When Lord and League Batman argue over ethics, they had this little exchange.
Lord Batman: Think about it. A world where there's no crime, no victims, no pain. [...] We've made a world where no eight-year-old boy will ever lose his parents... because of some punk with a gun.
League Batman: (drops batarang) You win.
Despite all that, the Justice Lords end up being de-powered and hold prisoner under the watchful eye of a reformed Lord Batman.
In yet another ironic but mostly unrelated twist, when the government caught wind of the alternate universe, they started the DCAU version of CADMUS, which is rather similar to Lex's 33.1 labs on Smallville.
And, as you should know, Oliver gets to wangst his way through season nine. While it is probably not the worst thing in that unspeakable horror of a season (I'll have to say, I have subconsciously repressed the memories of that
Dork Age), it is still not entirely welcome. In another contrast, the Justice League Superman's greatest fear is becoming his counterpart (Divided We Fall), and other Leaguers like Batman and the Question has doubted if he will make the right choices. When the main universe's Lex Luthor apparently got the Flash killed, an enraged Superman grabs him and his eyes begin to glow...Wonder Woman rushes forward, but Batman stops her, knowing Superman has to make the right decision himself. He delivers this line.
Superman: I'm not the man that killed President Luthor. Right now, I wish to Heaven that I were, but I'm not.
There are also a few similar instances; also in Justice League, the Huntress tracks down Mandragora, the crime boss who killed her parents when she was a little girl, and attempted revenge only to discover it was a decoy (much like what Oliver did in Bride), and got kicked out of the League for it. Later, when she comes face to face with Mandragora, she decides to turn him back into custody instead.
In the Injustice: Gods Among Us comic, the Joker used a kryptonite-enhanced fear gas to make Superman hallucinate that he was facing Doomsday - but when he tackled it into space, the gas wears off and it turns out to be Lois, and he was completely helpless as she dies along with their unborn child. For the extra kick, the Joker rigged a nuclear bomb to her heartbeat and in the next instant, Metropolis is utterly destroyed.
Joker: First Krypton, now Metroplis. People you love tend to blow up, don't they? That's why I like you, Superman, you are much more gullible than - (gestures to Batman) You think you can have a family. That locking me up would magically reform me. And they will be safe. So big, so dumb. (laughs maniacally) Now run along, so I can break out of here. I've got lots of planning to do to top this. I know it is soon, but...think you'll ever love again? Maybe you won't kill your next family...
Superman had enough and kills him. And it all goes downhill from there. And he is the final boss in the video game that follows the comic.
During the Infinite Crisis, Maxwell Lord kills the Blue Beetle and makes Superman see Batman and Wonder Woman as Brainiac and Doomsday (supervillains just love messing with his head). Bound by Diana's lasso of truth, Maxwell Lord reveals the only way to free him from his control is to kill Lord, which she did. Unfortunately, Brother Eye caught the whole thing on tape and activates 200,000 OMACs designed to exterminate superheroes. And it all goes...you know what I mean.
Well, that is what I could think of at the moment.
If you happen to be really displeased by now (which I somewhat doubt given your persistence), go and watch
this random video that just came off the top of my head.