I really enjoyed it. There were some problems, but overall, I liked it. Definitely worth seeing, even if you don't like what's going on with the Mandarin character.
As for the Extremis...
My buddy thought it ripped off Batman pretty hard. He was kind of disappointed.
My question is whether they will continue adventures of Iron Man.
I'm kind of hoping they do. Yeah, I know he'll be back for Avengers, but I'm kind of hoping they keep making IM movies. I know the 3 story arc is clean and nice and works well. But they've done a nice job of not making it too reeruned. And as long as they don't get too over-sweeping and huge enemies, I think they can do some decent movies yet. Marvel has earned enough credit to let them try another.
As to RDJ as Stark, I think they need to leave it alone, if RDJ can't do it anymore, they need to leave it alone. RDJ is it.