Unfortunately, there are only so many pot jokes and the rest of the humor in this movie, along with the plot, is predictable. Of course the plot is going to be predictable--I did not expect too much there, but the immaturity of some jokes does not make me smile.
James Franco tries to resurrect his career after sinking in Annapolis. He does a pretty decent job, but I do not find him to be funny. For example, I do not think sticking your thumb out of your fly is humorous. The predictable plot makes the 1 hour 50 minute running time see superfluous. This flaw was also apparent in Knocked Up.
Seth Rogan seems to be headed for the same path as fellow funny men Will Ferrell and Adam Sandler. Make a few good movies and then just repeat the same gags and jokes to score at the box office.