Robert Downey Jr. plays a fantastic role in both of the Iron Man movies. He just has the charisma that makes the character more intriguing and hilarious. I like how they play down the ego of Hammer when they make him look like a jackass when he tries to be "cool". For a man to be able to be super smart like Tony, as well as being confident (in his case narcissistic), its almost like he's just the coolest guy on the planet, other than his personality disorders.
I thought it would have been awesome if Scarlett ended up with Tony, but she was a good foil to the romantic tension between Tony and Pepper. She was so hot in this movie as she always is and to top it off she kicked butt and took a lot of names.