It's getting bashed because Adam Sandler is in it and that automatically turns people against the film. I bet had anyone but him been in it that it'd be getting better reviews.
people HATE Adam Sandler. I haven't watched a film of his since the Waterboy in the last 90s, but what I've heard is that he really hasn't evolved his schtick at all. And while those of us who were in high school and college when his first two comedy albums came out found that stuff hysterical back in the day, we've grown up and no longer find it that funny. Sandler, on the other hand, hasn't grown up and has basically just continued doing his thing. I think he's also caught some serious flack for the Ridiculous Six development stuff where Native American actors walked off the set due to the humor he employed. Basically, I think folks are just friggin' tired of him.
The sad part is Sandler has proved that he has range by the few semi serious parts he's had like in that Punch Drunk Love movie he did that got good reviews, he just seems to prefer to play morons.
I don't think that it's so much as his fans prefer to see him playing the moron. Sadly for Sandler, the number of people who are still fans of has gotten much smaller since the peak of his career and it's getting smaller every year. As the one article stated, if he was smart he should start transitioning to different kinds of roles before it's too late, if it isn't too late already. Smart comedic actors like Robin Williams & Tom Hanks did this, Steve Carell is doing this and have taken on or taking on more serious roles while others like Chris Pratt and Ryan Reynolds are starting to move over to the action star type of roles.