Not a fan of the whole Extremis premise. It puts the movie in a bad position because we end up with a weak enemy for IM to fight and a weak enemy always makes for a poor movie. Really a guy already using Extremis and Tony having to use it as well does nothing for me.
I would rather they adapted Armor Wars, which would have had the added benefit of allowing them to expand the Marvel Film Universe by introducing many foes in various types of armor. Crimson Dynamo and Titanium Man at the top of the list.
Staying away from the Mandarin while PC also is a mistake as far as fandom is concerned.