I'll only speak to the ones I've seen in person.
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Kane Positives: Nose for the net, great speed, great passing, great hockey sense. Plays big when it counts.
Kane Negatives: He's small. Not a particularly physical player. Still has some growing to do defensively (but what barely 18 year old sniper doesn't? Not many!).
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Van Riemsdyk Positives: Good height, good speed, great shot, great hands. Knows how to keep his linemates involved. Excellent on special teams (leads the U-18s in PPGs and SHGs).
Van Riemsdyk Negatives: He needs to fill out, but with that 6'3 frame, I expect he will. He appears to me to have made significant strides in the physical aspect of his game since last year when I first saw him, but he still has room to grow there (that will come with filling out I imagine). He's also a fairly raw player. A bit of a late bloomer. Definitely needs a couple years at UNH before he's NHL ready, IMO. But he'll be a stud when the time is right.