If the game is short - a first-person shooter, for example - that's not really an issue, since there's plenty of time to play through the game and write about it. Because game reviews need to go live before the games themselves come out, reviewers usually get games a week or two before they come out.
To understand why Mario + Rabbids: Sparks of Hope is my current go-to game, I need to explain a little bit about how the video game review sausage gets made.