First off, some spoilers ahead.
Sadly, I found it quite disappointing. I love the first movie, it showed such love for the characters and had a real sense of fun. This one though felt as though they were on autopilot. Sure, the cast are good and they each have moments when they shine (love Sam Rockwell!!) but the second half of the movie especially felt rushed, with no real sense of threat from the baddies (who are taken out far too easily).
Scarlett looks fantastic but would the story have suffered if she hadn't been there? The drunken Iron Man party scene was embarrasing. It reminded me of the dancing Peter Parker in Spidey 3.
The final battle at Expo might as well have been from Transformers. Next time, who ever directs it, please have something other than Iron Man vs. Baddie in big armour suit. It's boring already. Surely there's more to IM than that.
What did I like? Well, as I said the cast are great and some of the dialogue was very sharp. The Monaco scene was fantastic as were the nods to Cap America and Thor.
All in all though, while entertaining enough, it was a big drop off from the charm, excitment and fun of the first one. I think it needs a touch of darkness. Not 'Dark Knight' dark but we need to see Tony deal with problems in a human way, not just with tech. The blood disease stuff in this makes me doubt if they'll go back to deal with the alcohol problem from the comics and deal with it in an adult way. The Tony Stark of these movies could never, as the film in fairness says, lead the Avengers. Time for him and the films, to mature into something tougher and more substantial.