Awesome trailer.. Marvel really knows how to sell their movies.
Since i already know about the Extremis plot and the multiple armors this is the first time that i see them in action and it's brilliant. Loved the Hulkbuster style armor (if it's indeed a Hulkbuster as opposed to a generic heavy duty combat design) and all the others.. since they began releasing specialized armors in the comics i've always been a fan of them.
Downey Jr. seems to be at the top of the game again, Special Effects are state of the art (of course) but it also seems there will still be a human component to the movie.
The only thing that's bothering me a bit is The Mandarin. In this trailer he comes off as very cheesy (especially with the delivery of that one line) and i fear we may get another rather weak/cheesy villain.
I loved the more recent iteration of the Mandarin in the comics (when i happened to grab one a while ago) that had the Mandarin as more of the chinese counterpart of Stark.. business suit and all that. Hammer in Iron Man 2 could have been that but they wrote him as a buffon so there's that.
Kingsley is an amazing and capable actor so i hope they've written a good role for him.
Additionally i wonder if they will use this movie to start up the alcoholism character aspect of Stark. It seems he's really torn up mentally after the Avengers movie and he always was quite the drink guy in the movies so it would be a good opportunity to lay the groundwork of Iron Man 4 if it will happen (and i guess it will even if Downey gets sick of the role which he's not even hinted at.. he seems to enjoy Tony Stark).