I saw it last night, I really liked it. My thoughts on it mostly land on "Dear, God, Marvel/Disney give RDJ whatever he wants to keep him as Tony Stark!"
It was better than the second movie, but still not as good as the first one. Certainly a movie that I think didn't stick with the "the third movie ends/marks the beginning of the end or reboots the franchise" stigma that's common in Superhero movies. (Granting that Superman and the first Batman franchise got to a fourth movie before things were so bad things had to stop.)
Thoughts on some topics being discussed concerning this movie:
The Kid
Kids in movies annoy the heck out of me. It's one thing if its a movie mostly centered around kids where a degree or to of precociousness is expected it's another when a kid is in a movie basically being an adult. (See: Short Round in Indy.) Kids in movies are also often used as fodder for the villain to cause trouble. Here? The kid was nicely used mostly thanks to RDJ's interactions and treatment of the kid.
The Mandarin
I'm not a reader of Iron Man, or any Marvel books honestly, but I can certainly see why fans are disappointed here and I sort of agree with them. This treatment and use of the character was a cop-out and, really, the studios had to see the pissing off of fans a mile away in doing this. Why use the character at all if you're not going to actually use him/do him right? It strikes me as a tease to get fan-boys in the door (since the trailers and promotional material gave no indication of this and highly suggested the Mandarin was the heavy in an "expected" sense.) I'm not bothered by it, again, in part to not being a reader of Marvel and in part I'm not that kind of "Fan Boy." (Plenty are ticked on the direction the Star Trek movie reboot has gone. And while it's not what I'd like to see, it's not angering me.)
There were other bothersome aspects the movie had but all-and-all I liked the movie and left the theater satisfied. It wasn't the movie-boner the Avengers was this time last-year but it was a nice effort. My movie-boner comes in June with "Superman."