I think his descision making needs some work. Hes got the flare, no doubt about it. And he has vision that Schenn will certainly never have, but he tends to go for a lot of hail mary passes, and can turn it over alot. Thats what happened in the begining of the season, and in the playoffs.
Now I realize its understandable for a young kid to do that, but my point is he still has a lot of flaws to overcome. Take away the final 10 regular season games, when he had 12 points, and his stat line is 14 points in 50 games. Not bad at all for a rookie teenager, but all of a sudden, he doesnt look that better than Schenn, if better at all
Actually I think as far as Karlsson's bad decisions go, it's more occasionally he misjudges when is an appropriate time to try an Orr-style rush. But he'll also get better at powering through in his skating as he grows stronger.
Over-all, he had 47 give-aways in 60 games, which is obviously worse than Schenn's 41 in 79, but understandable given his role is quite different.
Per the points thing, I'm not sure why it's pertinent to take away the final 12 games when he finally got the hang of running a powerplay. And another thing is, pretty much inherent in the PMD name, a puck-moving defenceman's worth is more than just the points he puts up. Sens fans started raving about Karlsson's play considerably before he was productive, which should give you some indication of over-all play. I'd say that apart from on the powerplay, he was as good or better in January than he was at the end of the year.
Another thing, not totally related to your post, is that the Sens' powerplay was atrocious before Karlsson sorted it out. We were fighting for 30th over-all PP in the league with guys like Kuba, Campoli, Alfredsson, Shannon (*shudder*) and raw(er) Karlsson on the points. I suspect Schenn's powerplay production would not mirror Karlsson's even if he were given similar opportunities.
EDIT: I forgot, this was supposed to be about Karlsson's defence.
I agree, his two biggest weaknesses defensively are his scrawniness and sometimes over-confidence seeping into his decision-making. Positionally, I can't recall anything like a 2-on-2 situation where he was where he wasn't supposed to be (apart from maybe in his first 9 games). I do recall he misplayed a 2-on-1 against Ovechkin and Semin, though *gasp*. One positional thing he needs to learn is what to do when the other team establishes a cycle, because sometimes he stands at (clears, haha) the front of the net and watches before identifying who to take. Once he does, though, he's a pretty relentless/tireless 1-on-1 defender.
The strength thing will come - if you look at the photo of EK and the 5'11" Alfie at the Alfie 1000 ceremony, EK stands at least an inch taller than him, so he's obviously got the frame. And the decision-making should be tempered with time and with Gonchar's mentoring. The positives defensively are that he's an excellent skater, which helps him make up for mistakes sometimes, that he has a good stick, that his skill helps him out on defence (like Doughty's does, though to a lesser extent now), and that he's a determined defender. That he shied away from contact a little later on in the season was noticeable for a time after coming back from a shoulder injury, but he compared himself to Niklas Kronwall at the draft and does have something of a mean/hitting streak - if you watch the Victor Hedman pre-draft video, you'd see at some point a little yellow cannonball (Karlsson) flying through the air trying to take a Canadian player's head off. I wouldn't be surprised if he eventually became a pretty good open-ice hitter, and he definitely got involved with some Penguins during the series: Malkin he got a few good shots on, but the Mike Rupp selection was probably something he should have re-visited.