Ryan Gosling can be a good actor, but 90% of his characters are as follows:
Quiet guy that stares longingly, talks in a quiet tone then stares more. Roll credits.
Booster Gold is lively and energetic, therefore he needs to be played by someone who is also lively and energetic.
Now, if Gosling played Booster like his character from The Ides of March, then that could potentially be good, as he actually talked at a normal volume and was lively and energetic in that movie.