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Consider the other side of the coin: the devs are important to consider, too, because it is part of their workflow, and ultimately their responsibility to jump through these hoops. Yes, it would be good to have every game thoroughly documented, but that friction will make devs less likely to want to put effort into categorizing their game. It's better to implement a 'subpar' content rating system that is actually used than it is to implement a content rating system that is in theory ideal but in practice inconsistent and subpar in its own ways.

The players don't see the rating system directly, they see the result of collaboration between system & dev.

I'd actually like to see an end-user contributed tagging system similar to how Steam does it.  You have the basic tags added by devs and then additional tags added by the users (with inaccurate tags being reported if needed).