Con Pilot has put it very neatly in it's context. I would go further, and say for the Japanese Nation as well it was in the end a good thing. More lives were lost in the B29 firebombing raids than at Hiroshima or Nagasaki and had an invasion taken place the firebombing raids would have intensified resulting in even greater civilian deaths (The RAF was preparing to join the fight).
Assuming the initial assault to be successful the the Allies would have had to fight their way yard by yard through Japan, the 'collateral damage' to civilians would have been huge. (Look at the newsreels of Okinawa ). It would have dwarfed the Nuclear numbers.
The USSR only decided to declare war on Japan at a VERY late stage . They no doubt would have invaded Japan from the North and they (or a puppet a la North Korea) would still be there now, as they are still in some of the very northern islands . In other words it would have been rather like the division of Germany.
The 'Bomb' allowed the Japanese to surrender with 'face' after all they had 'only' been beaten by 'unfair' technology ! They were also allowed to keep the Emperor
who was not tried as a war criminal . And finally it allowed them to play ,very successfully post war, the victim conveniently burying the truth . Discuss !