If you haven’t read it before, don’t read the Wikipedia summary; read the actual story. It’s easy to google and pretty short. Isaac Asimov said it was his favorite story he’d written. He imagines the entire history of the future of humanity, to the end of time, in a few pages. Really a marvelous story.
Damn it, I wish I read this comment before I read the summary. I had chills at the end. Maybe I should read some Asimov...
Nightfall is a decent story though. But yeah, The Last Question is in a league of its own. It's one of my favorite short stories ever along with The Library of Babel by Borges, The Great Automatic Grammatizator by Roald Dahl, and "Repent, Harlequin!" said the Tick-Tock Man by Harlan Ellison.