It's vacation time again

Next week on Friday Mrs Clegane and myself are traveling to Vietnam (with a 2-day stopover at Bangkok and a couple of additional days to visit Angkor in Cambodia)

The places we are going to visit in Vietnam are:
- Hanoi
- Hue
- Saigon
- Phan Thiet (for a couple of days on the beach to relax at the end)

Our intinerary includes a 2-day trip to Halong Bay and a 3-day trip to Ba Be National Park from Hanoi (unfortunately we do not have the time to visit Sa Pa) and a day-trip to the Mekong-Delta from Saigon.

Any tips/recommendations - practical or regarding "must-dos/sees" (that perhaps aren't found in the typical travel guides) are highly welcome