I put the RoK’s up there will Israel’s military. They will kick serious butt and like doing it.
Yes, the fact they have universal military service for men (that they rigorously enforce) makes a difference. So almost all men from their twenties up have had some sort of national service (although a bunch are doing their two years of service in the national police—considered a branch of the military—and some as firefighters or other emergency personnel). So although Korean men gripe about having to be in the military, if there were a national emergency or attack, they are basically all trained already if there has to be an organized response.
Ironically, I recently had a Japanese woman say to me that that is the difference between Korean men and Japanese men, and why a lot of women in Japan now find Korean men attractive. She said that because of the military service they are more masculine and physically fit. (I think Korean men are also naturally taller and bigger than their Japanese counterparts, which also makes a difference.) Interesting comment, because historically the Japanese really looked down on the Koreans as inferior (and Koreans, especially the older generations, often still have pretty bad feelings towards the Japanese because of the Japanese occupation from 1910 until after WWII and the historic discrimination against Koreans by the Japanese).
I should have mentioned that the RoK forces got quite a reputation in Vietnam. Basically for taking no prisoners and responding with overwhelming force. If the Vietcong attacked, the RoK troops would just go back into the village they were hiding and level it. If civilians were harboring the Vietcong, too bad for them.
After what they went through in the Korean war, the RoK forces had no love for any form of communism and responded appropriately.
So while the libbies will talk about RoK “atrocities” in Vietnam, the fact is that the Vietcong and North Vietnamese got the message and instructed their troops not to attack the RoK forces. So you had the anomaly that while U.S. forces were often under attack, they would generally leave the RoK forces alone.