Di Maria has been playing well, I don't really rate the guy but he has impressed me, he certainly moves off the ball a lot and he has nice skills and a decent shot on him.
Higuian was poor against Costa Rica, he hasn't played much football in the past couple of months for Real Madrid so he is very rusty, Messi set him up with a couple of one-on-ones that he couldn't put away. He should improve with more game time, I like him in the side as he provides the team with a genuine target up front both to hold the ball up and in the air.
The guy who has impressed me the most though is Aguero, I've never rated him, thought he was all hype, but he has been very good