The short version: I enjoyed it.
Robert Downey Jr carries this film. Jeff Bridges does an excellent job, but it's Downey's familiar irreverent style that sells it. Mostly when he's the only actor on the screen -- bizarrely, the second-best characters in the film are actually the robot arms in his workshop, and they only work because of Downey's dialogue.
(So, yes, the script takes much of the credit too. This is a fun movie.)
There was a fair bit of discussion over in communicator's journal about the portrayal of women here, but I was reasonably happy with it. There aren't a lot of characters here: Downey, Bridges, the sidekick, the villain, Gwyneth Paltrow, and the questionable reporter. The males outnumber the females two-to-one, but that's a surprisingly good balance for a superhero blockbuster, and the good/bad distribution's actually better on the side of the ladies.
If we look at the character of Stark himself, it took me a while to work out how I felt he was being written, and it's like this. He's technically a genius, but emotionally he's about fourteen or so, and a sheltered fourteen at that. He's got no idea how to connect to anyone emotionally, let along adult women, and he runs away from it a lot. He's very much a patriot, and in the way that teenagers do, he sees everything in black and white. When we meet him, he genuinely believes that by making the best weapons he can for the US military, he's making the world a better place by keeping the soldiers of freedom safer. When that ideal is torn away, he's still naive (believing his company's better than it is), and he still hasn't grown emotionally. At no point during the film does he actually grow into a mature human being - he just has a better idea of what his company really does. Naturally, he applies his talents to addressing it directly, personally, rather than, say, trying to change the people or the society or whatever.
And that brings me to Pepper Potts, as portrayed by Paltrow. I thought she was great. She's a real adult with no illusions, but that doesn't mean she doesn't have dreams or fantasies. She's smarter than Stark, and wiser by orders of magnitude, but still human. And because of all that, she can see the honesty and the desire to Do Right in the immature man, and between that and his undeniable style and charm, she's fallen in love. However, she's not an idiot, and is fully aware that when there's a possibility of Stark crossing that as-yet-unbroken line, she knows that it would be disastrous now, while he's still immature. She's torn between the hints of a fantasy coming true and the knowledge that it wouldn't really be her fantasy, not while he's got another decade of maturing to assimilate.
Despite all that, she carries herself with dignity, and continues to keep her boss as her boss.
The film has problems, of course. The cartoon nature of a shell suit stopping you from injuring yourself when you and it slam into a wall at 200mph come to mind, as does the rapidity with which the villain manages to get the hang of a suit when we spend half the film watching the hero do the same. The sidekick never grew on me, either. But I can forgive all of this, just like I can forgive sentient AIs, over-complex assembly droids or holographic GUIs. It's a cartoon, and a superhero cartoon at that, and it didn't look silly.
And Downey may be playing the same character as Kiss Kiss, Bang Bang, or even Ally McBeal, but I still thought it was great.