I didn't realize we were on a code share flight from Seoul to Hanoi until we got to check in counter and they couldn't issue boarding pass even though it was a through check-in for till Hanoi. In our booking itinerary it was printed as Korean air with a small print that said operated by a junior. It wasn't so bad but the hassle of going to another terminal to board and being in a smaller aircraft after a long flight wasn't the best.

Very comfortable flights (a change of aircraft in Seoul). Very pleasant flight crew and good food. Flights left promptly. Very good business lounges at both Heathrow and Seoul. Excellent value.

Checkin was good.
Checking counters at Seoul airport were crowded and they had one small counter for collecting boarding pass if you have checked online but you cannot drop bags.
Staff were helpful.
Inflight was good.

In USA, you always stick to one airline to get mileage points & other benefits. However, you’ll never know what’s being offered from other airlines until you try one for the sake of it. Korean Airlines is one of them, and you’ll see the difference in service. From check in, to boarding the plane, and stewardess’s services in the plane are way better than in USA. They’re young, pleasant looking, smiling, nice uniforms, eager to please, assist and help customers. They seem to be constantly busy working serving customers in their needs whether assisting in putting luggage in the top bin, find their seats, serving seconds, or even making sure the restrooms are clean and with refreshing smells. And I’m sorry to say that US plane services are lacking and stewardesses are lazy and because they’re experienced and older, they don’t seem to care.
p.s. I left my jacket in the plane, and I just tried to ask in my return flight 10 days later and walahhhh!!! they have it, showed me the picture and gave it to me as I boarded the plane.

I have to say I was very disappointed in their lack of friendliness. Lack of food as well for two long haul flights. Trip over was really bad service for 12 hours we got only two small meals one hour into the flight and one hour at the end of 11 hours, no snacks. The return trip the plane was a big bigger and seemed to have more room and more food on offer. The sad bit was both directions the lack of smiles from the staff and lack of interaction with the customers which I found rather bizarre as I really thought they would be really friendly. Not sure if it is the language barrier but they did speak English. Would not jump at a chance to go again unless the price was really cheap. Just having to ask for water and they filled a plastic cup half full and disappeared, no sticking around in case you wanted more. Disappointed.