I love it, you have to use such different tactics due to the guns being stronger. Squad rush is great on all the maps.

The density of vegitation also means there is very little long range sniping, a huge let down to a sniping buff like myself.  Vehicle combat is pretty much non-existant, and the helicopter is so weak that two guys with AK's can take it down pretty easily (I'm not kidding here). 

On the pc version, I seem to be getting head shots with assault/medic way more often, not sure why.
 
And you can take the helis down easily with the jeep mounted weapons or the boat weapons (which seem overpowered).

Probably my favorite thing about the Vietnam expansion is how much more balanced the vehicles are.  Such a difference from the core multiplayer game.  My #1 gripe used to be how overpowered the helicopters were.  Now helicopters will go down fairly quickly as long as your team lays down some small arms fire on them.  I do not miss the days of trying to place a tracking dart on a helicopter that's doing circles around me at a 100mph while it's shooting rockets.  Tanks now having flame throwers as the secondary fire instead of the ridiculous overpowered machine gun  seems to have made a massive difference as well.  No more tanks just sitting on top of a mountain sniping people with it's secondary fire.