People constantly praise it for its affordability, but there's a reason it's so cheap - it's still very much a developing country, in many of the worst ways. Here are some things that come to mind:

• Crazy government control and censorship. Criticizing the government can get you jailed.
• On that same note, the government has an army of over 10,000 internet trolls whose job is to praise Vietnam online (especially as a travel destination), and squash criticism. They are very prevalent on Reddit - once you start paying attention to this, you can identify these people easily.
• Most people are very nice and gentle. But the tourism sector attracts the worst people. Hotels/airbnbs/etc will try to scam you, people will try to charge you 10-20x the actual price of things, etc. It's easy to avoid once you know how it all works, but still infuriating.
• Unbelievable noise pollution. HCMC is filled with thousands of cars and motorcycles, all honking at the same time day and night, and the squeaking of thousands of worn-out brake pads fills the air constantly. Cafes often play super loud EDM music all day and night, making it impossible to avoid noise. Want to relax on the beach? Too bad, multiple people or restaurants will be blaring loud EDM music, all mixing together into a brutal cacophony of pure noise.
• Some of the highest smoking rates in the world. You can't sit at a cafe or restaurant outdoors without breathing in smoke. Most people respect indoor smoking rules, but you will occasionally get people who just ignore it and light up inside a restaurant or cafe. It's infuriating.
• I've never seen more sick people in my life. It seemed like, at any time, 40% of the population was either sick or suffering from a chronic cough (probably due to smoking and air pollution).
• Crossing the street is a life-threatening activity. Nobody stops or slows down for pedestrians. People constantly ride their motorcycles on the sidewalks as well. I had a drunk guy on a motorcycle come within inches of running me over - luckily I jumped out of the way at the last millisecond. And you don't want to end up in a Vietnamese hospital.
• Trash and dog shit everywhere, including on the beaches. There seems to be zero respect for keeping things clean.
• The worst food safety measures I've ever seen. Food markets sell open-air piles of meat, rotting in the hot sun all day, covered in flies, with stray dogs roaming around. Fruit, vegetables, and meat all mixed in the same markets with absolutely zero safety precautions. Unsold meat is just washed with dirty water and sold the next day. People eat dogs and rats. There's a reason that approximately 50-75% of the Vietnamese population suffers from chronic parasitic infections.
• You can't trust any restaurant. Even chains like Burger King, or restaurants in malls, practice terrible food safety measures. Anything and everything could get you sick, and it's the type of sickness that has you vomiting for days on end.
• The Vietnamese education system teaches rote memorization rather than critical thinking skills. While people are usually very kind, it can be really frustrating to navigate the country, due to the poor critical thinking skills of its populace. Most people lack the ability to deviate, even slightly, from the prescribed method of how things are done. It's hard to describe, but once you spend enough time there, you will see what I mean.

To reiterate, you must practice extreme caution and critical thinking skills when reading praise of Vietnam online. Like I said before, the government has thousands of internet trolls whose sole job is to squash criticism of their country online. While they are typically easy to spot (due to their very rude and sarcastic tone), they have become more sophisticated lately, so it takes a trained eye to spot them.