I read half your post and had to go to the bathroom. I thought about the ROK troops I had heard about from a buddy. Came back and read the rest. From what I have heard, they are still very hardcore. I'm not going into war stories, rather, I'll recount my experiences under less stressful scenarios.
Personally, I knew some British scouts. Armor scouts, like our Cav units. They were some hardcore guys, in the field and out. Six of us went to Canada, and ran into six of them. We formed an impromptu super-squad of beer inhaling war athletes. When some dummy came in and messed with one of our guys, then followed him into the bathroom with bad intentions, those guys jumped up and had his back before I could get up. Thanks to them, no fight occured. These guys were infantry, and so were we, and that brotherhood extends to our allies, we learned that. From what I could tell, their violence of action, athletic prowess, and their military bearing were so close to our own, the only real difference was they had round dog tags, spoke with an accent, and hated their rifles (the L96 bullpup or whatever --they hated the French weapon even more!). They wanted their FAL's back.
Later that looooong weekend in Canada, some guy threw his girlfriend through a plate glass window. It cut her up pretty bad. He tried to finish her off, but we stepped in. Again those guys shined. Long story short, we patched her up, called the cops, and I cornered the guy. No Canadian citizen would help or even call the cops. It fell upon us. We almost got the Soldier's Medal for that. Those Brits were some good guys to have around, and we all just clicked. I'd like to have had them in my unit.
Canadian snipers are bar none. Those boys can shoot! I'd rather go up against any average American sniper than an average Canadian one. I think those boys spend more time at the range than do our own. Maybe I only got to see the good ones, I don't know, but every one of them could shoot.
I've met others and heard other stories, but not worth mentioning really. I did train with a brigade of Japanese soldiers in Yakima once, they were very well disciplined. They look more laid back than they did in WWII footage I've seen, but not by much. They could take a lot of ribbing too, and we sure dished it out.
Iraqi soldiers suck. Period. For some reason, most of them are almost untrainable. I don't get it. If we are waiting for them to stand up and secure their own country, we are going to be waiting a long time. They have no discipline, they won't show up on time (or ever, flip a coin) won't shoot back, don't have your back, help the enemy, etc. The Iraqi school age children are more reliable.
It all basically boils down to this from what I can tell. There are infantry soldiers and there are other soldiers. In the West, the infantry guys are very similar, more alike than not. Perhaps that is why I could always click with those guys, but not my own Coast Guard cousin that lives a few miles away. Now him, HE'S a foreigner! Go figure.