How many people do you see score 30 goals (and another 7 assists or so) while playing on the wing? Only Ronaldo, Messi and Neymar have scored that many in a season while playing as a winger (off the top of my head), in recent history at least. That's with him just having turned 21. Ignoring his productivity, he has a great shot, had the best record from set pieces in Europe last season, is fast, physically strong, is creative, scored 2 goals in his first ever world cup when he was 20, has the drive to become the best that some lack perhaps, etc.. Really not sure what else you would want?
So many notable people from the netherlands have come out and said how big of a talent he is, how he is already a very good player but his potential is enormous. He has the stats to back that up, and has the perfect manager to get the best out of him.