I don't know.. I'm leaning towards the ones not liking it are mostly fanboys, but then again, SHH was extremely positive towards the film so people here had high expectations. I know you guys probably don't look at AICN for X3 stuff, but in their public talkback, a majority of the people (these are the same ones who wouldn't shut up about how sucky this film would be) were pissed at Harry because they were impressed with the film- the ones bashing it on AICN were the ones defending it after they saw it. So a lot of it depends on epectations.
Having said that, I think the fans are the ones with the highest expectations (I was a little "blah" after seeing both X2 and X3 in theatres for the same reason, I had very high expectations for them), so those were the ones who would obviously see the most dissapointment with the final product.
I'm not even going to try discussing critics- their in positions to act as quasi-public figures, so there will always be some bias. For the most part critics enjoyed the film (from everything I read), just not as much as X1 or X2.