I think Keldon Johnson will be an effective 2/3 wing. I don't see him as a star, but a solid 2-way player who can guard 2 - 3 positions. He's got good size with the potential to grow another inch and add to his 6'9" wingspan. He's a good shooter with a high, compact shooting stroke that's consistent when he gets his feet squared up. He finishes well at the rim and has some touch with a floater out to about 8 feet.
I'm trying to think who he compares well to, but I think he'll be better than Kentavious Caldwell-Pope and better than Allen Crabbe. If things go well for him, he might be comparable to Devin Booker, but with better defense. I'd rate him maybe just a notch behind Culver from Texas Tech, but I think Johnson is a slightly more explosive athlete and better defender than Culver. Johnson is more catch-and-shoot, while Culver can create better off the bounce.