I don't get how movie critics claim a movie is or isn't objectively funny. A comedy's success relies almost entirely on weather or not it's funny, and humor is a completely subjective thing. What's funny to a certain critic isn't funny to a certain viewer.
The only way I can think of where a critic says he finds a movie funny is a useful statement is if a reader has been following that critic for a long time and discovered after many movies that they have a similar sense of humor, and therefore what's funny to the critic will most likely be funny to that reader, based on past impressions. That's it. for everyone else a critic saying a movie is funny is just one guy that thinks it's funny, in no way does that mean more or less than any other random guy saying it.
TL;DR: think for yourself folks. Do you like Seth Rogan movies? Stoner comedies? Christmas movies? These are the factors that should determine weather or not you go see this movie.