Non default game settings, whether use of co-op or multiplayer or fixing a control scheme, are like seasonings included on the side of a restaurant meal. While the food might taste delicious with them, if the meal tastes poor without such seasonings, it brings up the question of why such seasonings need to be added and weren't already added into the food by the chef, reflecting poorly on the food and the skills of the creator. On the other hand, refusing to eat said food when it tastes perfectly fine with salt and you have been told so beforehand is a touch snobbish and wasteful. Thusly, a review that mentions what changes to the settings or which modes to use will improve the perception of quality and functional quality of the game of those who purchase the game because of said review. However, if reviewers look at information before playing the game, then they will have more difficulty being objective, because the reviews and would flavor said reviewer's opinion of the game's quality.
So, while we can mention said reviewer should try the food with salt, pepper, or some precise mixture of honey, vinegar and ranch dressing, and he should mention it in a post review edit so that the reader doesn't suffer as much as the reviewer did, we cannot blame the reviewer for not knowing to try it with such a seasoning, and he has every right and responsibility to have lower opinions of the food as a result.