It's not THAT bad
The original is probably my favorite comedy of all time. The sequel is probably not on anyone's top ten list of favorites. If you go into the sequel hoping it will be as good as the original, you will obviously be disappointed.
If you take it for what it is, this movie actually had some funny moments. There just haven't been that many good comedies that have come out recently, and this was better than most of the garbage Hollywood has given us lately. I think this movie just gets horrible reviews because it's being compared to the original.
Have you seen Zoolander 2? Now THAT was a disaster.