Tony Stark, still stressed out from the events the occurred in The Avengers, picks a fight with a mysterious terrorist known only as The Mandarin. Stuff happens and he eventually wins.
I really enjoyed the first Iron Man film, it managed to be a witty counter-point to the dour hero cliché. Iron Man 2 was weakly plotted rubbish, but Tony Stark was the best part of The Avengers. So it is at least theoretically possible that Iron Man 3 could have been a fine film. Sadly, the film makers seem to have forgotten what made Iron Man so much fun.
First the good parts. Iron Man 3 is well put together and contains lots of fairly well directed action. Fans of things zipping around and exploding will not be disappointed. The acting is appropriate with Ben Kingsley's Mandarin being a particularly entertaining standout.
The main problem with Iron Man 3 is the plot. The villain is suitably comic-booky, but his plan doesn't really make a lot of sense and Tony Stark only gets involved for the most tenuous of reasons. This leads to a long sequence where Stark bonds with a kid who teaches him the real meaning of Christmas. Or something. I don't know, it was pretty lame and saved only the kid actually being a pretty good actor. There are a few laugh-out-loud moments but the film jumps tone so often that it is had to make out what the producers were going for, action comedy or just gritty action. It is a little jarring.
Of course, it all comes to a suitably grand finale which might have been a neat surprise if it wasn't spoiled in the trailer. At least Pepper Potts gets her own subplot, even if it goes nowhere. Also, Iron Man 3 contains the single most blatantly silly product placement I have ever seen, I hope Oracle paid well because they certainly got some screen time.
Iron Man 3 is not a terrible film, just a very forgettable experience. Recommended only if you like this sort of thing.