I really enjoyed it. I don't know anything about Iron Man's story arcs in the comics, so thankfully I was not disappointed by the Mandarin Twist (sounds like a soft drink). That said, please don't hate me when my following comments come from the frame of reference of IM 1, 2, 3 and the Avengers
I do agree with those that said the Mandarin could have been a Ledger-(wait for it)-dary performance. It took a couple scenes before I believed that it actually WAS what it was, and not just an awesome misdirection by the "real" Mandarin. But, that's not what we got, and I think that what they did instead totally worked within the context of the film. After all, everyone assumes that the bad guy is Other these days, and in some ways it was worse to see someone co-opting that for their own perverted purposes.
It did make me sad to see the arc reactor removed from Tony. Why didn't he have it done earlier? My understanding was that if they tried surgery he wouldn't survive. So my inference from the final scenes was that after Tony fixed the Extremis to save Pepper, he also injected himself with it so he couldn't die while they removed the shrapnel. Hence his statement of "I AM Iron Man". Maybe I was reading too much into it, because if that were the case I would have expected to see some final scene where he and Pepper both have the glow.
As far as Pepper Potts, it was really nice to see her do get to do some bad-assery. And for giving an easy cosplay for the ladies.. an Iron Man suit arm, about a million situps, and a black sports bra

Not sure how I feel about her having an actual super power now (again, I assume Stark stabilized Extremis, not figured out how to remove it from her). I liked that her strength came from her intelligence and devotion to Tony. It was a nice touch at the end when, after going all ape **** on Killian, she was instantly worried about what happened to her.
Anyway, I came really late to the Iron Man game; I avoided it because I didn't think my heart had room for another "billionaire playboy" after Batman. Then all the IM builds on here had me appreciating the design of the suit, then I saw the Avengers and really understood what his character was like, and then I became obsessed with the first two movies. So this was the first IM movie I was excited about, and for me it lived up to my expectations.