Seth Rogen is really not funny. Not only is he not funny, but he acts like he is this big star. He's not Will Smith, Tom Cruise or Brad Pitt, yet Rogen acts like he is on their level. If you're going to have an ego say something funny, even Conan had a few decent lines.
The Rose Byrne and Eric Hutchinson segments were pretty forgettable as well. When there is no Touriffic or Tramstastic or whatever the segment is called, or no Twitter Tracker the show really suffers, as you could have cut the Rogen interview in half to make room for that.