If a joke needs so much explaining, it's probably not worth cracking in the first place. All the little inside jokes don't justify the final episode in and of themselves.
When I think of all the episodes, even some from this season, that seemed so effortlessly funny and then compare with the final episode, I'm left dismayed.
And while I'm thanking about that I'll think about this: why bring back Bookman and make him so damn unfunny?