The penalty was correctly given. Yes, Robben went to the ground in a theatrical fashion, but he was quite clearly fouled.
There are quite a few people who have it in for Robben, and certainly based on his play throughout his career there is cause for displeasure at his whinging and diving. However, the last couple of years he's been a lot less prone to this sort of behaviour and he's really grown as a player. I think people should give him more credit. At the moment he is one of the best, if not the best, player in the tournament.
That being said... Boy, I was anxious watching this game. The orange team looked absolutely dreadful at the start. De Jong getting injured really put a dent in our defense, and the new defender that replaced Janmaat was horrid. No offense to him, but I hope this was his last game in the orange jersey. Things really turned around when the team started to play 4-3-3 and we got rid of the dead wood. It helped of course that Mexico had completely given up on trying to play football and their coach had his team go into ultra defensive mode the moment they were in the lead. Awful decision by the Mexican coach. And then Sneijder, of all people, scoring the equalizer, and Huntelaar who hadn't played even a minute previously scoring the winning goal. Love it.