I enjoyed the movie, and I had a fun time watching it. But in the end it just didn't engage me on the same level the other Marvel movies have so far. I'm sure I may get hell for this, but I enjoyed Iron Man 2 more than this, I felt Mickey Rourke was a much better villain over Guy Pearce.
And as for the Mandarin switch, I have no connection with him in the comics, not read a single Iron Man story that features him, and yet I was disappointed with the "twist." He was being built up as this scary terrorist that seemed very real based on past events and yet was still a bit of fantasy, then they take that away from us and give us another businessman in a suit.
Like I said though, I enjoyed watching it, there are actually quite a few bits I really loved. Namely Iron Man saving the passengers of Air Force One, that was a moment where I wanted to stand up and cheer. I also liked the assault on Stark Mansion, complete with Pepper wearing the armor for a time. I also loved all the references to The Avengers and how Tony had to deal with the aftermath of that.
I think this is a movie I definitely need to see again, as it's troubling that I can talk of so many instances that I enjoyed from the movie, and still have mixed feelings on it.