For years, many fans of Kiss Me Deadly, and Robert Aldrich fans in general, regarded this film's abrupt, disorienting, and apocalyptic final seconds to be a bold and creative statement for a movie released in 1955. This original theatrical ending, which was supposedly due to accidental film damage (but maybe not), is better because it is much more brash and ends the way an atomic explosion should. Instead, the "restoration" (with Mike Hammer and Velda watching it all from a nearby beach) makes the atomic explosion look more like a gas explosion.
Aldrich was known for some abrupt endings and beginnings (think of the crying jack-in-the-box at the start of "Baby Jane"), so appreciative viewers were right to assume that this was the ending the director intended. I, therefore, thank the projectionist or whoever else enabled us to see this supposedly "mangled" version for so many years. Sometimes directors don't know best.