I posted this in another thread, so let me just post it here.
It appears that Vietnam is stronger than we thought. The ability to place Forests down earlier really offsets having to place Specialty Districts on Woods, Marshes, and Rainforests. The Thanh is actually a good place to gain Adjacency Bonuses for both it and adjacent Specialty Districts. It not being a Specialty District makes it easier to plan your Specialty Districts around it to get the sweet Culture and Tourism. It also works with the Culture theme for Vietnam. The Voi Chien looks like a pretty powerful replacement for the Crossbowman. Extra Movement, can move after attacking, extra Bonuses toward defense, what's not to like about it? Lady Trieu's ability really gives it a sense of Defensive War and guerilla tactics without being memeish.