He is not the Canadiens' best prospect, that's for sure, but his calling card is very high skill. As a recent draft pick (2012 2nd round, 33rd overall), he's in their pool of top prospects yet to knock on the door for an NHL job. But the Canadiens have several forwards in their system like him, and Collberg has a ways to go
In terms of where he fits the Islanders, he is still in Sweden at age 20, playing for Frolunda and going through those growing pains of a young player "playing with men." He doesn't yet get a lot of minutes there, so that and his size (5'11", ~185 lbs.) will factor into when the Islanders would want to bring him to North America for AHL tutelage. (He played two games with AHL Hamilton at the end of last season.) The Canadiens signed him to an entry level contract which began this season.
His upside is a top six winger, but his destiny is anything but certain.
Here was Habs Eyes on the Prize discussing the right-shooting winger last summer:
Sebastian Collberg is a hard prospect to peg exactly. In peer-to-peer competition, whether in Swedish juniors or head-to-head against the best of his age group in international play, Collberg has ranged from solid to dominant.
On the other hand, there isn't that much to brag about on Collberg's play in Swedish adult leagues. Collberg struggled to crack a very deep and talented Frolunda forward group and as a result posted only six goals and nine points in 35 games, particularly because many of those goals were actually from scoring the winning shootout goal. It was not particularly uncommon for Collberg to dress but not play, or only see 4th-unit time in 2012-13.
Since that posting the 2013-14 season has gone similarly, with three goals and six assists in 40 games for Frölunda in the Swedish league. Playing back with his U-20 age group, he also put up six points in seven games at the World Junior Championship.
Elite Prospects profiles his strengths and weaknesses like so:
Collberg is very skilled forward with great wheels. Doesn't shy away from the high-traffic areas and knows where to go to score goals. Initiates contact with defensemen and has excellent one-on-one moves. Posesses an elite wristshot, which he can release in a hurry with great accuracy and velocity.
Needs to add more bulk to withstand the physical game at the men's level. Lacks ideal frame and defensive play needs improvement.
The Good: Collberg is a plus skater who has a great combination of agility, acceleration, and top gear speed. He's a good if not great puck handler who is creative and can control the puck very well, be it on the sideboards on the PP or in tight spaces. Collberg has a tremendous shot and while "quick release" if often overused in scouting circles, his really does stand out. He also shows solid vision on top of being a gritty player who drives the net regularly.
The Bad: His size is worrisome and his frame is pretty slight. Despite his good work ethic, he projects as a replacement-level physical player. Despite the low minutes, his production in the SEL is worrisome although he did produce in international play. He will also sometimes get tunnel vision in terms of finding his teammates.
Projection: His ceiling borders between a fringe first-line winger to a great second-line winger.
Anyway, at his age Collberg remains a good prospect, and still a reasonable trade chip for a deal like this. Wrote HEOTP in trade deadline prep:
"If Bergevin truly wants to make a splash, one of Sebastian Collberg, Artturi Lehkonen, Charles Hudon, Tim Bozon, or Martin Reway could fetch serious return."
So yes, Collberg is still young -- he turned 20 in February -- but he's yet to shine against older players which means it's the same old drill Islanders fans know well: Has potential, might realize it, might not.