The good news is it's much better than Iron Man 2, which was a muddled mess that pretended most of the first movie never happened. The plot's clearer and easier to follow, the action is actually pretty well-realized, and while I dreaded having three Iron Man comic refs in the movie that I utterly hate (Extremis! The Mandarin! The woefully stupid Iron Patriot!) it didn't grate on me too bad.
The bad news is, it's not very good, and indeed, barely an Iron Man film. Trying to build a movie around the importance of Tony Stark and Pepper's Potts' relationship is never going to work, because they have the phoniest love affair in a movie brimming with phony shit (I believed in the notion of the genetic whatever stuff they injected you with that let you grow back limbs and burn people or whatever more than any of their scenes together) and despite the movie trying mightily to sell me on how theirs is a True Love, I didn't buy it any more here than I did in the other movies they've been in.
I'd be willing to let that slide if the movie moved along a little more briskly, but then there's that interlude in Tennessee with the cute kid, which stops the movie totally dead and it never quite gets its momentum back. The movie seems to want to have this come across as very emotional even if it's kidding it at every opportunity, but since it never commits one way or another, it feels more like they're just killing time.Plus, the kid is pretty much just a ball of "cute kid" cliches and never really becomes his own character.
The villains are a mixed bag. I know a lot of people have whined about the twist with the Mandarin, but in all honesty, I loved that part--the Mandarin totally sucks and was used appropriately. The other two bad guys don't make much of an impression (mostly because the movie is too busy trying to set up a big third-act reveal to give them the requisite amount of character for it to be the SHOCKING SWERVE it's supposed to be) but I'm sure the brief for the third movie was "look, do whatever, just make sure it's not another guy in an Iron man-like suit again this time," and in that, it succeeded.
The final battle with the multiple armour suits is OK in theory, but it never quite opens up and becomes as awesome as it should be and soon devolved into "Stark fights a guy, suit gets damaged, he hops into another suit, lather, rinse, repeat." The out of armour action sequences are actually pretty good and have some really clever bits in there, but the movie doesn't seem all that determined to apply the same sort of imagination to the armour combat sequences.
So in all, it doesn't make the mistakes Iron Man 2 did, but makes a whole bunch of new ones instead, plus it's an Iron Man movie which is trying really hard to be something other than an Iron Man movie, so while it wasn't wrong footed enough for me to hate it, I can;t say I'm any any hurry to re-watch it again.