Critics should due everything they can to give an objective criticism of whatever they're reviewing or criticizing. For a gaming example, criticizing a puzzle game for not having an open world isn't a valid criticism. That's the critic's bias stating what they wanted rather than an proper evaluation of the product.
But what would be a "proper" evaluation in that case? The fact that the game has puzzles? What if the critic find them too hard? Saying that would be objective, or subjective? Would his lack of skill with puzzle-based games (assuming no other critic is around) void his review completely? How could he measure the fun factor in this case without his personal bias? Is a personal bias something that should be reflected in the review, or not?