The Kings traded Linden Vey for the 50th overall pick in the 2014 draft, and then used that selection on Roland McKeown. Vey was not a minor loss - he was a good center prospect, who had scored over a point per game in the AHL as a 22 year old. He was 7th in the rankings last year, and probably would have finished 5th or 6th this year. McKeown is 13th, which says something about what we think of the trade. Not that McKeown was a bad pick - he might be a big part of the Kings' future. Or he might not. It's just that Vey looked close to establishing himself as a good NHLer, and with McKeown it's kind of hard to know.
As a first attempt at quantifying McKeown's chances of making the NHL, I looked at every defenseman who was drafted within 10 selections of McKeown from 1990 to 2006. I didn't want to include forwards in this analysis because historically, forwards and defensemen pan out at different rates (defensemen tend to be riskier). It turns out there were 104 defensemen drafted from picks 40 to 60 over that time. Of those, 35 (33.6%) reached 100 NHL games played. About 26 (25%) of those were "successful" picks, in my opinion (the bar was not high - that's counting guys like Matt Carkner as successes). 3 (2.9%) became superstars (Zdeno Chara, Duncan Keith, Shea Weber).
So that's a good starting point: based on McKeown's position and draft status, he has about a 25-30% chance of working out. That's not that great; I'd probably rather have Linden Vey than a guy with a 70-75% chance of contributing basically nothing. On the other hand, that is just a starting point. There might be signs that McKeown is better or worse than most defensemen drafted around pick 50. Let's look.
One thing in McKeown's favor is that a lot of people thought he deserved to go higher than 50. In January 2014, the consensus was that McKeown would be chosen around pick 10; while his stock fell late in the year, in Bob McKenzie's pre-draft ranking - based on the consensus of scouts - McKeown was 25th. That's an assessment the Kings evidently agreed with, as Michael Futa said after the draft that the Kings had considered McKeown at pick 29.
I find all this encouraging - it's good to know that a lot of hockey people think McKeown has first-round talent, even if he ended up sliding a bit.
There's more reason for optimism in his OHL stats (available thanks to @butyoucarlotta). His 1.3 points/60 at EV was eighth among 2014-eligible CHL defensemen, slightly better than first overall pick Aaron Ekblad (1.2 points/60). Filter out the guys who weren't playing top-pairing minutes, and McKeown jumps to third (behind only Anthony DeAngelo and Julius Honka).
It's true that, at both the NHL and Junior level, points are less useful for evaluating defensemen than they are for evaluating forwards. Still, point totals do tell us something. Rhys Jessop has shown that, while defensemen are inherently risky and high point totals do not guarantee success, low point totals do basically guarantee failure. Defensemen under .55 points/GP in their draft year only make the NHL about 10% of the time. McKeown is at .69 points/GP, so he's above that threshold.
There is a bit more CHL information available. McKeown had an EV GF% of 66.10%, which is quite impressive. More importantly, McKeown did well relative to his team, which put up only a 52.2% with him off the ice. That's a promising indicator of a good two-way player, but single-year GF% is notoriously unreliable and subject to randomness. It's difficult to know to what extent McKeown was good and to what extent he was lucky.
McKeown also played the top competition on his team. I think the importance of quality of competition is often overstated, but it's still a nice sign that his junior coach showed trust in him.
The scouting reports say that McKeown's skating is his best asset. McKeown can lead a rush and has offensive instincts good enough to quarterback a power play. Scouts praise his defensive positioning, but universally criticize his lack of physicality. He has decent size though (6'1", 197), so that might improve with time. He clearly projects as a two-way defenseman. So whatever McKeown is, he's not the next Colten Teubert. That's a good thing.
McKeown will spend 2014-15 in the OHL. Even if his development goes perfectly, McKeown is many years away from the NHL. There's lots of risk here. I think Vey is very skilled, much closer to the NHL, and probably a better bet. But once the Kings decided to trade Vey for the 50th selection, I think they did a pretty good job with the pick. McKeown has promise.