And many seem to think that the movie pretty much ignores everything that happened in The Avengers which would be a bit lame.
I'm not sure where you're reading your reviews, or maybe I just didn't notice which events are ignored, but the main subplot for IM3 was Tony dealing with the PTSD he developed in New York after those events, and it was in no way subtle about it.
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George Carlin wrote:
I think it’s the duty of the comedian to find out where the line is drawn and cross it deliberately.