Rykov and Reunanen, who just came over from Europe are good prospects. Robertson, who was a second round pick this year looks like a good pick. And one of last years first round picks, Nils Lundqvist, had a really good season in the SHL. There are Lindgren and especially Hajek, who played briefly in the NHL last season, Fox, who they got from Carolina and DeAngelo, who is still young.

Hajek, Fox and De Angelo are three of the four young guys I referred to who are already up on the NHL roster, so they aren't "prospects" on the farm. Miller and Lundqvist aren't signed yet, so they don't count, either. I haven't seen any prospect service rating Rykov, Reunanen and Lindgren as anything more than "maybes." I think the Rangers farm is actually pretty deficient in defense prospects unless at least one of the two Europeans pans out.

Well, Miller is in college and won't sign until after his junior year (probably). Lundqvist is playing in the SHL against men and there is no need to sign him until you want him to play on the NHL. They are both 19. Rykov, after two KHL seasons is in the mix to make the team this year. Reunanen is a little more of an unknown and Lindgren has less upside.
There are no guarantees but that's still a lot of players especially with Trouba, Skjei, DeAngelo, Fox, and Hajek 25 or under on the NHL roster.
On the other hand, they have a few top end forwards with great upside (Kakko, Kravstov, Chytl in particular) but not a lot quantity.