Well for one thing the vehicle controls are terrible. I've played Bad Company 2 and the helicoptors controlled far better, I have no idea why they decided to take a step backward and make them worse. Jets are useless, as you can see by watching the jets fly around but only get about 2 or 3 kills for an entire match.
The matchmaking system is by far the worst one I've ever seen on the 360, and when you do get into a match it will sometimes put you in the opposite team from your party, which is a massive design flaw that needs to be fixed. Even worse is most of the time it wont let you switch sides because "The servers would become too unbalanced".
Another thing is the spawns. 4 times I spawned right beside an enemy, once I spawned with someone directly in front of me who saw me spawn, and another time I spawned in the same room as 2 other guys. That's insane, you should never see people spawn.
The game also seems to be designed for HD TV's only. If you don't have one then you're going to have to move your face about 2 feet away from the screen if you want to see anything.
And finally the gun combat. For as much as I hate COD it's better than this. You don't get shot in the back nearly as much as this game. No skill involved in the kills of battlefield.