Superman rescues a spacecraft that is studying the sun from being destroyed by Luthor, who has taken control of one of the artificially created humanoids on board. But there's a price--Superman's cells are now overloaded with power and the sun that gives him his power is now killing him. So he does his "Bucket List", which includes revealing to Lois Lane that Clark Kent is really Superman. He takes her to his fortress of solitude where he gives her a one-of-a-kind birthday present-- a potion that will give her his powers for 24 hours. It's the best present she could get.
There are some odd characters from the future, Samson and Ajax, who know of Superman's impending death--and a glimpse of the Superman from the 84th Century. But Lois and Kal El can't have children since they are two different species. Or can they?
The animation is lame, though it does cover all the major plot-points from the two ALL STAR SUPERMAN graphic novels upon which this animated movie is based. It's a stand-alone story that doesn't tie into any other Superman continuity (especially the animated television series or JUSTICE LEAGUE series). All in all, it's just "O.K. SUPERMAN".