I have been to Vietnam over 40 times. Yes 40 times and I have seen Hochi Minh City, Halong Bay, Hoi-An & Hanoi. My favorite part of Vietnam for touristy stuff was Halong Bay but its definitely a one time thing. My favorite part of Vietnam for food is Saigon or most commonly known as Hochi Minh City. The restaurants are more diverse and cater to non meat eaters.
I pretty much only have photos of food because I think Vietnam is fabulous for food. Street food is amazing.
I would forgo certain things such as spa services. I have never had a professional positive experience.
Vietnam is definitely a must see because its still so 'countryside' but just with great internet service!
Be careful crossing the street! Enjoy