He has some Kopitar in his game, but I think Kopitar is a very direct player (which Matthews does have in his tool box), but I do think Matthews has a fair amount more flair to his game. Guys with his agility combined with his puck control at 6'2 216 is very rare. I'd add, he seems to be more of a goal scorer than Kopitar. Now, if he can get a defensive game 90% of Kopitar I'll be ecstatic, he has the tools to, but putting it all togeather is another story. Pretty sure Crawford was quoted as seeing a lot of different people but he like the Kopitar comparison but said Matthews has more offensive ability, but had a fair way to go to approach Kopitar's defensive ability.
I personally see a lot of Crosby in his game in regards to puck control in tight spaces and lower body strength, but not the same vision and passing. Like most elite prospects, his game has a bunch of comparables for certain traits but isn't a clone of anyone. It is like how McDavid has a lot of Bure in his game but clearly other influences such as P. Kane but with the ability to play center, or how Eichel has a very undefinable game (while clearly being elite).
In regards to Matthews, I've seen a bunch of comparisons from guys throughout the hockey community. Off the top of my head, here are the ones I remember.
"Better Skating John Tavares"-Benning on a radio program
Benn, Kopitar and Sakic by Crawford
Kopitar and Toews-many places, but particularly Button
Ryan Getzlaf by Schiefele post-WC