I don't really know anything about Rangnick
Why is everyone going crazy over him?
Because he was a major factor in the development of the RB system which has produced a lot of talent and brought in many players, for cheap prices and turned them into quality players. Look at the list of players posted on the previous page that he was linked to bringing in.
Now admittedly that is more of a case for him being DOF, but considering that is exactly what we need and is arguably more important than getting a new manager, I think a lot of people are hoping that whether he is manager or DOF that he would bring those skills.
I also think that since he turned down Chelsea for not meeting his requirements when they offered him their position that if he came to Tottenham he would do so only if Levy gave him guarantees on how things would work. He has been linked to other jobs and turned them down so it doesn't appear that he is desperate to just get any job.
Edit:
Forgot to add his influence on a lot of the coaches having success around Europe and a style that is having success and likely the way most fans want to see us play.