Some of them I can't recall having seen yet, so I'm biased toward those who I have unfortunately:
I never really cared much about the hype for Young, didn't let it bother me too much, so I decided when I got the chance at the USO to finally see the kid play, that I should go. Sat through first set and a half against Guccione, walked around a bit and then came back to it, and in that match I liked a lot of what I saw. Yes, he had massive crowd support, but I think he needed it to help him with that initial breakthrough. A lot are quick to dismiss him, most without ever having seen him play, based on reports of ego and hype
I think he has potential. Gulbis I also saw for the first time at the USO, twice actually. His first round match with Starace and then his fourth round against Moya. In parts he played well, enough for me to be optimistic. As for the rest... I'm slightly indifferent. I can't remember having seen Zverev or Bolelli play, and because of that, at this point I am surely underestimating them. Querrey.... I'm just not impressed with. He's not really too young anymore... he's an '87 just like Murray and Djokovic. Capable of a run here and there on hard courts, but it's not like he's going to win a Slam or a Masters with his game.
Actually I am not sure if I see anyone in this group really performing that spectacularly. They're all a bit hit or miss, not a single one of them is a sure thing.