The dishes and flavors in Vietnamese cuisine varies as you travel up and down the coast or inland of Vietnam.
The farther North you travel, the colder the climate becomes and the flavors and ingredients indigenous to this region reflect that. The growing season is shorter than it's southern neighbors where the sun shines more often throughout the year. Due to the colder nature of this climate, spices and fresh vegetables are limited and the locals rely on preserving and stewing these ingredients to carry them through the year. Because of this, flavors tend to be very simple, less bold and lack extremes in spice, bitterness, & salt. The ingredients speak for themselves and are used in respect to its seasonality.
Phở is a good example of this. This Vietnamese specialty was originated in the North where the preferred preparation includes a simple broth that is cooked with bones, a simple meat, and (banh pho) the specific flat rice noodle used in the dish. That's it people. No sprouts or big heaping mound of herbs or chili that is enjoyed in the South. Just a simple soul-soother on those cold days.
We have been to Northern Vietnam when a chill is in the air and the rain came down hard! We sought shelter in a stall that had just the remedy we needed. The menu was filled with warm, savory dishes like Vietnamese rabbit-curry . Here, rabbit is stewed until tender with subtle flavors of turmeric, coriander, cinnamon, and other ground spices.
I'm not talking about an extensive curry repertoire like you would find in Indian or Thai cuisine. Vietnamese curry is lite and much more mellow and reflects a certain "peasant-stlye" of eating.