In this issue, well ... things really fall apart. I do not mean with the charcters either. I mean with the truck size holes Alan Moore seemed compelled to place into the story. If Ozy only attacks New York, that would not stop an attack. Our enemies would realize it is a moment of weakness and take advantage of the situation.
Also , at the end of the day, no one would believe Rorschach. He is considered a nut job. There would be no reason for John to kill him. On the other hand, he lets Ozy walk. Even knowing what he did, how he killed millions of people. There was no reason to punish Rorschach for his belief, and no reason for Ozy to be kept alive after what he did.
Also, don't you think that terrorist groups around the world would try to take credit? If it were world wide, then it could be explained the way Veidt wanted it to be. The way it happened, it just doesn't make sense. This is still a great story. I just do not think the ending holds up to the rest of the series.