I can never figure out for sure if Rutherford was a true believer (who really beleived that he was God's chosen) or if he recognized that he was running a massive racket and just having fun with it. He seemed to make doctrinal changes for the sake of differentiating the organization from other Christian groups. I think Franz took the JW religion seriously and wanted others to do so as well. He didn't clean everything up (such as restoring a lot of holidays and religious observances) but he did try to roll back some of the more egregious stuff.
He probably should have scrapped Rutherford's penchant for predicting the end, but I suppose he couldn't help himself.