As a Canucks fan, my understanding of Forsling is that he's a lot like Clendening at an earlier age.
-strengths are in moving the puck, quarterbacking the power play and he has an excellent shot
-weak on defence
-small for a pro defenceman (was listed at 5'11-175)
-needs to work on physical strength
-skating is "good"
At the world juniors he was on Sweden's 1st pp unit, where he had a spectacular tournament. At 5 on 5, he was on Sweden's 3rd defensive pairing and was very ordinary.
His ice time on his Swedish team has been declining as the season went on according to the weekly prospect reports at canucksarmy.com.
It seems likely to me he's a few years away from the NHL but has considerable upside potential. That seems a lot like the reports on Clendening when he was drafted, with perhaps Forsling's strengths (and maybe his weaknesses) being more pronounced at that early age.
As for Clendening, he's just finished his 3rd game with the Canucks this evening. In those 3 games he's gotten a fair bit of power play time (the Canucks haven't scored on the power play in what seems like years now) and has mostly played on a 3rd defence pairing. The last 2 games his even strength defence partner has mostly been Ryan Stanton, with whom he'd partnered for Rockford in 2012-13. Overall he's averaged 18:24 time on ice including his power play time, with 1 assist, he's + 2 (while the Canucks as a team during that time are -3), has 4 shots, 1 hit, 3 giveaways, no takeaways. The Canucks have lost 2 of those 3 games and as a team have given up 3 more goals 5 on 5 than they've scored, plus an empty net goal was scored against them.
2 of his 3 giveaways were early in his 1st game with the Canucks. He's been pretty sound since then.
My own opinion is the same as many posters here-the trade was mostly a time shift as the Hawks had too many defencemen to easily fit Clendening, who is waiver eligible next season, while the Canucks had a void from several years of not drafting anyone that developed into an NHL player. Canucks got an NHL ready player that wasn't going to crack the Hawks roster while the Hawks got back a younger prospect with similar strengths and weaknesses that they can keep in Sweden or Rockford for a few years without exposing him to waivers. The trade seems to fit the teams' different needs.
For a report last summer on Forsling, see
http://canucksarmy.com/2014/8/18/prospect-profile-16-gustav-forsling. Obviously, Forsling's stock has risen as a result of the WJC.