In college I was part of a field of study called "Japanology" for two years. I thus believe I can talk with a small matter of authority on the subject.
As others have already stated, the isolationist nature of the nation has prevented a lot of inter-country warfare from occuring. It's worth noting that during the majority of Japan's hsitory this isolation was not self-imposed, but rather a result of the difficulties in traversing the seas with the primitive crafts then available.
For a long time the Japanese mostly had a culture of warriors, not soldiers. What this means is that battles resembled more closely a collection of loosely connected 1 on 1 fights and small skirmishes rather than the formation fighting we see in ancient and medieval times in Europe, Greece, etc. This evolution made sense when seen against the cultural backdrop of the nation; however, when the Mongolians once invaded Japan they brought with them an actual professional army, and the Japanese were quite powerless against it. The Mongolians didn't play by their rules and just "dishonourably" cut them down as efficiently as possible. Thus the Japanese troops were routed, but the Mongolians--who couldn't believe the ease of their victory and thus expected a trap--returned to their ships. That night a huge storm swept across the coasts of japan, a storm of catastrophical proportions, and the majority of the Mongolian fleet sank, leaving the men to drown. The remaining forces hastily departed back to the mainland. (this is known as the kamikaze; the God Wind).
Oddly enough, the second Mongolian invasion was stopped by a storm, too.
Anyway, this historical account shows that the Japanese of that time were not all that fiercesome in open warefare. However, it is the honourable warrior culture that many admire, the idea that war is more than a few square formations meeting to cut each other down, but rather battles between skilled warriors to prove who is the better man. This appeals to a lot of people.
It has to be said, though, that after the Sengoku period (shown in Shogun 2: total war, partially) Japan had apparently moved away from that quite a bit, with the peasantry (ashigaru troops) forming into professional armies and the like. Indeed, when Hideyoshi later invaded Korea they blitzed to the Korean capital in no time at all, and not even the intervention of the Chinese could halt their armies. Instead, their conquest was foiled by the difficulty of maintaining supply lines and guerilla tactics.
Even then, though, a direct comparison is very hard. It seems strange to us that the Japanese used almost no shields, but they just had a completely different warfare style, relying on mobility more than the protection a heavy shield could offer, because when you're facing circling archery warriors on horse back you're far better off with mobility than with being able to block arrows from one side, apparently.
So yeah, the Japanese warrior culture was very different from our own, and that's why some people feel drawn to ti. We can debate its merits all day, but in the end, their fighting style fight their needs perfectly, as the western style did ours. Letting the two battle each other is a pointless (but fun) mental excercise.