Papa (born 1992), Draxler (born 1993), Matip (1991) and Holtby (1990) all have potential to be world class. It's also likely that Ninis will join next year and Schalke will have the most talented team in Germany.
I was especially impressed by Papadopoulos so far, he should get more playing time.
His performance against Benfica
There are also some Holtby videos on YouTube, this year he was on loan in Mainz.