What they should have done

They should have had Tony utilize the incredible resource of the Stark Expo to save his life, rather than doing it under house arrest. The whole movie was basically a tee-up for the Avengers, and they missed the opportunity to demonstrate tangibly how working as a team could be beneficial for a traditionally lone-wolf character. Also, the concept of the Expo never ended up going anywhere except as the final set piece, and briefly at that.

It would have been cool, too, if Vanko had been controlling the drones from an airplane, so that way in the climax, Stark could have done the inverse of the intro, which was him flying from a plane to the expo (so he'd fly from the drone fight at the Expo, up into a plane where a Whiplash confrontation would begin)

But I'm not a writer for Marvel.