Prepare for a long, drawn-out answer that I think will leave everyone unsatisfied. I honestly can't tell you how the rest of the world thought after it happened, but I can give you some insight into the US's feelings and maybe speculate from there.

So despite staying on the sidelines, the American people were watching the war unfolding in Europe with close scrutiny. Americans broke into two political "camps" during the early years of WW1; the "Atlanticists" (Pro-British), and the "Pacifists" (Those wanting neutrality; a small radical faction wanting an alliance with Germany). There was one more camp (forgot the name) that wanted a middle ground between joining Britain and strict neutrality, (ie. President Woodrow Wilson and other "League of Nations" types). Though they began to swing more towards the side of the Atlanticists since the US and Germany began butting heads as the war went on, and they realized that their desire for a international council to police the world and prevent war would be possible if the Entente powers won. Anyway, the Atlanticists and Pacifists split the ideological opinion of the United States mostly along nationalist/religious/economic lines:

Atlanticists (Pro-Britain): Mostly the upper-class elites of American society (rich people, bankers, merchants, wealthy business tycoons, etc.). Had strong support from "Crusader" Protestants (Protestants who believed we must defeat "The Hun" to save civilization and Christianity; and bring a total end to war forever). Also found support amongst American Jews (originally Pro-German until the Balfour Declaration; since Germany at the time was considered the most religiously tolerant European nation and Russia was clearly the most antisemitic). Also support from African-Americans, believing that supporting the US military would bring a positive image to them as loyal citizens, and may speed up the Civil rights process. The camp's main strength was in states on the East coast and parts of the American South-East.

Pacifists (strict neutrality, small minority were Pro-German): Political strength was from Americans who were not so well-off financially (since it were their sons who would probably have to fight the "rich man's war" should it come to that). Support was strong from German/Irish/Scandinavian immigrants, the urban and country poor, women, the elderly, Socialists and Anarchists, Non-Violent Christian Churches, the "Confederate" South, most Catholics, and most members of the Working class. Strongly held the Mid-West, Most of the South-East, and dominated the Western (but less populated) half of the United States.

The political battleground was especially heated by rival newspaper companies who would take sides based on whichever one they stood to benefit the most from, should it be successful. Powerful city newspapers with money, (New York Times, New York Post, Washington Post, I think some newspapers in Atlanta as well), tended to be strongly favored towards a Pro-British policy. The Pacifist papers, (the Newspapers of smaller towns and countryside villages, San Francisco and other Western city newspapers, Socialist, Pacifist, and Anarchist pamphlets; and I think most Chicago papers as well), with much less money and circulation had an uphill battle from the start.

The Atlanticists were able to shape American opinion much more profoundly than the opposition; and with vast amounts of money and control in government agencies (Committee on Public Information), began a propaganda campaign to convince Americans that only a war-alliance with the Entente powers could save civilization. The long propaganda campaign using movies, pamphlets, etc. was able to throw mainstream America's support behind the British even before Congress declared war. The Pacifists (even with greater numbers) never stood a chance. So as the Atlanticists gained power, German offences against the United States and "European Civilization" were blown out-of-proportion in the press (whether the outrage was justified or not) to justify an American entry into the war. While British offences were either swept-under-the-rug or we given a positive-spin to lessen the blown, ie. Despite the British seizing an American ship and holding it's crew under arrest so they could search the ship, they couldn't have been more "courteous" about it.

Also the Black Tom explosion and the Kaiser's unwillingness to heed his staff's advice to warm the US up to an alliance or at least neutrality, (the Kaiser was absolutely sure that it was only a matter of time until the US joined the Entente and so didn't worry about playing to the Americans' every need as the war continued), definitely didn't help the Pacifists' cause. Neither did accusations of treason for collaborating with Anarchist-types, or the slander of disloyal immigrants (especially against the Germans and Irish), help either.

So it really depended on how one saw Britain, and that would determine how they saw Ireland. The general opinion amongst Atlanticists was that it was basically a foolish act of treason that caused unnecessary loss of live amongst citizens of the Empire. The Pacifists tended to see it as a justified, although doomed from the start; act of defiance against a bloody, war-hungry Empire that was a source of world misery. The Atlanticists saw it as treason by rightful British citizens trying to justify it with "Fenian" non-sense; if they even cared about the uprising at all. The Pacifists saw the Irish as their own independent people resisting a system of oppression, similar to the American poor resisting domination from the "robber-baron" rich.

My guess would be that Pro-British nations criticized it heavily, and neutral countries split between pro/anti-Irish rebels; but regardless still had sympathy for the Irish cause, even if they didn't support it. The anti-Imperial third-world nations were mostly inspired by the rebels, and held them and the Irish people in high regard; but only if they heard of the events. That would probably limit news of it to rebel nationalists inside the British Empire fighting for their independence from it.