The worst use of the time-travel reset button I’ve ever seen was the ending on John Byrne’s Superman/Batman: Generations 3. I was expecting that the ending in the 30th century would rely heavily on the Legion of Super-Heroes, and that we’d see the heroes somehow drive off the Parademons to begin their cycles of retreat to the prior century, which is the cause of everything we see in the prior issues. Instead, we get almost no screen time for the Legion, and Superman stopping Darkseid’s time travel plot before it can begin, which means that everything in the foregoing issues never happened, and leaving no plausible explanation why Superman would have found Darkseid and killed him (yes, you read that right) since the incidents he killed him over never happened either.
That ending was just a total mess. A major disappointment, given how good the first two “Generations” series were, and, quote frankly, that one was as well, if not for the lame ending.