Just had about 45mins on BC2 Vietnam - I'd say 6/10 on first impressions.
The weapons seem very, very accurate - my accuracy is easily double that of standard BC2 weapons. Obviously suffering from a complete lack of map knowledge, but that will come in time. Some maps have definitive choke points which are very difficult to get past attacking and easy to keep secure as the defenders.
Rush defenders have it the toughest. Pretty much ALL scenery can be shot through and blown up, so a ram-shack hut with an MCOM station in it provides zero cover for defenders and/or people trying to disarm it.
Of the maps I've played, the Yanks have a BIG advantage in terms of vehicles, etc. The heli-gunners are easy to take out, so there's a counter there - but good flyers really do kick ass on this.
And, pick the PPSh Russian made SMG. In all previous FPS games, this gun couldn't hit a barn door more than 20ft away, yet sprayed the target area with lead. In BC2 Vietnam, it's the new M416 imo. Definitely worth using.
D.