Gosling has that same quiet, monotone, almost pseudo-intellectual acting style in every one of his roles. I don't dislike him, and I don't think he's a bad actor, but he's definitely overrated and it's as if he's too shy to come out of his shell and really ACT.
Will Smith plays the same character in almost every movie. But he CAN play different characters, and very well. He's like Johnny Depp. I think they choose to play the same character over and over, but in those rare situations when they're thrown into a completely different role, they absolutely nail it.
That's the difference between Smith and Gosling based on what I've seen. Gosling has played characters with vastly different personalities but they still feel exactly the same.
So, basically, I feel like Gosling can't rewire his personality for a specific role like Smith/Depp can.