A friend and I purchased the Vietnam DLC last night and played it for a good few hours. Really enjoyed it. The map visual design is gorgeous in places, but the actual game play of one or two of them is really off. I can't mind the name of it, but the map with the ruins on it... what on earth is that about?! As attackers, you can't move from the initial spawn if the entire defensive team is 'sniping'. Even if you can get near the MCOM stations, the defence again have the upper hand thanks to the map design. Anywho, that was just initial impressions, but overall, I'm not regretting buying it.
EDIT - One thing I did notice that didn't seem to happen as badly on the main game proper was after one or two rounds, the losing team pretty much all leave, and the game doesn't balance. We ended up most times with the 'winning' team outnumbering the 'losing' team after just one or two games. We would then have to leave and find a new server to get into a balanced game. I don't remember that happening quite as badly on the main game.