I'm not super an expert on this, but I think I can give a sufficient answer, but if anyone else can do it better, by all means.

There's was a fairly large debate going on immediately after the war, as well as into the nuclear age, and to a small extent continues today, but the general consensus is 'no, but it saved American lives.'

At this point in the war, the Japanese navy is totally and utterly in shambles, and with the capture of Okinawa and Iwo Jima, the US could have easily engaged in a full scale invasion of Japan, and would probably have won. However, this was seen as a costly, in terms of money, as well as in American boots, strategy, especially in light of just dropping a huge bomb or two on them.

Also, the fledgling of the Cold War can be observed here, as you could reasonably argue that dropping the bombs was a form of posturing, hopefully discouraging the Russians from reorienting the charged Soviet war machine in the direction of the West, or even developing their own nuclear weapons, as it was known the Germans had been doing research into nuclear munitions, and since the allies had already divvied up the German research and researchers, it was a safe bet the Russians could be working on their own nukes.