I never really got that into the show.. Some of it wasn't very funny so I stopped watching it. I guess it's "American humour" I never really understood.
Fallon is just not good at telling jokes. Kinda sucks when that is what you are supposed to do on a late night talk show. The show is ok once you get past the fact that the format is screwed up. It is what it is, maybe he should go the route of Carson Daly and not tell jokes at all.