This is my issue with IM3. We have superhero movie that to me greatly diminishes what it is to be a superhero, or more specifically Ironman. For me part of the appeal of any superhero is that you don't just like them, you want to be them. (This should make a lot of sense on a prop and costuming site.)
When Tony first takes flight in the MK2 or when he blows up the tank after taking an artillery shell to the face, all I could think was "I want to be that guy."
In IM3 when Tony is running for his life from the extremis soldiers because they are literally karate chopping his suits in half, or when his latest and greatest MK42 is constantly falling apart and in need of a "recharge" from a car battery, all I thought was "I don't want to be that guy."
Simply put, they made Ironman a lot less awesome for me.