This has been puzzling me for a while. There has been a lot of media about the Vietnam war period, but not any that I am aware of about the years after. I was wondering how did Vietnam change, what were the major and minor reasons that it didn't end up like North Korea?
Sorry, could you clarify what you mean by "ending up like North Korea"? Việt Nam is still a single party communist state, in theory. In practice, economic reforms have moved it from a more-or-less communist agricultural state to a semi-centralized market-based state under single party rule, similar to China.
If you are wondering why Việt Nam has no single leader with a cult of personality like NK's psuedo-monarchy, that has it's roots in the party structure. While Việt Nam had and still has a very strong central leader, they aren't completely unchecked and it isn't (in theory) a lifetime position. That said, from about 1960-1983 power was almost entirely in the hands of the general secretary due to Lê Dưẩn's concentration of power. Dưẩn patterned his government after Stalin and but subsequent leaders have opened up government to some extent and made the comitee more involved in descisions, though the General Secretary is still the most powerful person in government by far.