The problem with a question like this, and the reason why answering it isn't easy, is because there isn't a "global reaction." There are a lot of sub-global reactions — people are divisible into many different scales.

So even asking, "what was the French public reaction?" is a very different question than asking, "what did French policymakers think?," which is different than asking, "what did French intellectuals think?" and so on. And you can substitute "French" for not only any nationality in the world, but also sub-national groups. E.g., the "American" viewpoint is not quite the same as the "African-American" viewpoint. This might seem pedantic but it is not — in fact it is quite interesting to look at these sub-national groups (and there is some great historical work on African-American attitudes towards nuclear weapons, as an aside).

And all of the above presupposes that we have some way to measure these things, which sometimes we do, sometimes we don't. So I could give you statistics from polls made on the US public in 1945, because the US did, at that time, have some systemized public opinion work being done. The problem is, that particular science was still in its infancy (Cf. "Dewey Defeats Truman," just three years later), and its methodology is sometimes pretty crude by modern standards ("we asked 500 Americans, by which we mean middle class white men who subscribe to Forbes, what they thought!"). And for most countries you might care about, we have no data whatsoever because nobody was doing public opinion polling there. So for example we don't really have any systematic way to know what the average Soviet citizen thought about the atomic bombs being dropped, because nobody asked them. (In fact, barely anybody told them that it had happened — there was almost no news about Hiroshima allowed in the USSR, and none about Nagasaki. Eventually these things became discussable and discussed, but I just point out that even the information access is dramatically different between nations.)

Now often we can characterize the opinions of individuals (e.g., I can tell you what Gandhi said when asked about them, or what Stalin's reaction was, or what George Orwell thought, and so on), inasmuch as they said or wrote things about them that were written down. And sometimes we have official statements that reflect "official" positions of governments or entities (e.g., the Vatican). But even here we often don't have information or it's very mediated through the lens of politics and appearances.

I know, I know: this isn't what you're looking for. You're looking for something simpler and more generalizing like, did people on the whole think they were a good idea, a bad idea, justified, not, etc.? The answer is: it's complicated. So the general US public opinion, from what we can measure of it, was something like: hooray, we've created some new weapon, and the war might end soon, and isn't this amazing that science and technology did such a thing, and we "won the race" with Germany (they weren't really in a true race, but they were told they were), and other positive emotions... mixed with questions like: What's next? Where does this kind of development lead? Should we really have obliterated two cities? Were there any alternatives? Will other nations get access to this? What will happen in the next war? Am I going to be a victim of this? Will all of this science and technology ultimately lead to the end of war, or the end of civilization?

I like to characterize this as "ambivalent" — whether the development was a good or bad thing wasn't always clear to people — though the trends of which of these views were dominant could change over time (once the war had ended and it seemed like the bomb had "done the trick," Americans were very in favor of using it, though over time they have become less convinced of its necessity), and the polls indicate that it is possible (as one probably ought to expect) to hold both positive and negative associations about the bomb at the same time in one's head.

Great, you say, that's what I want. OK, but what would a non-American have thought? Again, very hard to measure. The Koreans seem to have been thrilled — they hated the Japanese because they had invaded and enslaved them, so the more blowing up, the better. The Soviet elite were not super happy — they knew they needed their own weapon if they were going to be "equals" with the Americans. The defeated Germans were pretty happy it wasn't used on them. These are broad, broad characterizations and should not be given a lot of credence. There are always a multitude of viewpoints and perspectives.

Anyway. This is why I don't answer these questions, and why you won't find any answers (that are any good) out there. It's just not a great question, to ask about the "global reaction to X" — because "the world" doesn't think: its people do. And for most of human history (and really, even today) it's very hard to actually characterize that in anything but a superficial and probably misleading way.

The best single book that talks about shifting attitudes towards nuclear technology, mostly in the US but also with nods to a few other nations, is Spencer Weart's Nuclear Fear: A History of Images. It's probably the place to start if you are curious about this topic.