I'm spoilering things that most of us probably know but people unfamiliar with the comics may not. Don't want to ruin future happenings in the movies or what people may read. When it comes to the villian situation of the movie they were really stuck. Iron Man has a very disappointing rogues gallery, especially when it comes to using them for movies. The first movie used the Stane stuff. The second movie uses the "other guy with a suit" and the Hammer stuff. Without using "other guy in a suit" they were really only left with the Mandarin and the use of people as smart as Tony. I find Mandarin stories in the comics some of my favorite so I'll admit that I was disappointed by the movie Mandarin
I can see why they did it though in the sense of the Marvel Cinematic Universe, if they were going to use the Mandarin. They are laying out Thanos for the Avengers 2, so
Comic book people know those are different items and completely different stories but the general public would see Thanos as something that would've been done already if they used the Mandarin story completely. The other problem with the Mandarin is the character is that he is much better with over-arching schemes. If they were going to use Mandarin they would have been better off alluding to the Mandarin in the first movie (yes the terrorists were the "Ten Rings", more substantial than that) and doing more building of the character in the second movie with the third movie being the big plan/final showdown. Honestly they would've been better off leaving that character out all together if they weren't going to do something along those lines.
People talk about how they should have used the alcoholism story for this movie, and while I think RDJ would've done it great justice, they did a very small allusion to it in the second movie with the blood poisoning and recklessness. To an extent they cleared it up by the end of the second movie, sort of, so using the full blown story for the third movie wouldn't have worked as well as people hoped. Others have expressed disappointment in Tony
Overall it's not the best movie in the world by any means but it's a good popcorn movie that I enjoyed and had fun with. It's a nice bookend to the RDJ Iron Man movies and it's not near as rage worthy as the mouth breathers on the internet have been making it out to be.