I've flown VN two times: The first time was from NRT to SGN. The other time was from SGN to HAN, which I took because I had no other choice.

My experience with VN is similar to yours. The staff is extremely inefficient (clueless) and downright rude sometimes. They rarely smile and look like they would rather be somewhere else. I have no complaints about the plane though. Both times, I thought the planes were clean and the seats looked new.