This is an issue that has been debated (sometimes pretty viciously) time and time again, with varying results. Did it prevent a conventional invasion of Japan? Yep. Was it necessary or the best course of action? ... I don't know if I'm qualified to armchair quarterback that decision, despite my obvious genius. From what I've read (and this region was a specialty of mine in college) there are pretty substantial arguments for both sides of the should have/shouldn't have dropped the bomb. There are people in both the US and Japan (among other countries) who argue that it was the right/wrong thing to do, and which side people take might surprise you.
I will say that, despite the revoltingly biased Peace Park Museum in Hiroshima, I have yet to meet a Japanese person that held a lingering bitterness about either the war or the atomic bombings. That doesn't mean they aren't out there, but they're definitely not the majority of the Japanese people. Personally, I'd say it was a toss-up between the bombing and McArthur's constitution (specifically Article IX) as to which screwed the Japanese over the biggest.
As my Japanese friends would say, "The situation is difficult." And if you've met many Japanese, you know what that means.