So Australia had an early release of IM 3 and there are 16 reviews on Rotten Tomatoes. Good news - 14 of those are good.
Bad News: 2 of those are bad. And they basically say the same thing - the movie is too much of a comedy, not enough of a serious drama. Now, is that really bad? I think it'll depend on the person. This one: http://filmink.com.au/reviews/iron-m… clearly sound like a the ranting of an obsessive fanboy rather than a reasoned and thought-out revie, but the other one is more calm. I guess the members of the Church of Nolan (who, as we all know, is in a Holy War against the Church of Whedon) will hate it as it won't be deep enough.
So, in conclusion I think it's overall good news, and I guess a few bad reviews are a good things - they lower expectations to a level the movie can achieve.