Particularly for the purposes of itchio's community as it exists, I think it would be useful to - in addition to "is this NSFW or not" and "what (of a limited list of content warnings) makes it NSFW?" ask "is this game intended as erotica."
Furthermore, add an icon marker to games flagged as NSFW even when a user has noted that they wish to see these games.
I want to see art games whether or not they include NSFW content, but by turning on "show NSFW" most of what's added is niche erotica targeted at someone who is not me. (I'm sure the intended consumers of those games are likewise irritated.)
Being able to filter out topics that one desires not to be exposed to - for example, I really don't want to see naked ladies, but am fine with the reverse; lots of people feel the other way around - would also be nice, and that's a level of specificity past the list of specific content warnings already described. (It would have to be enforced laxly, because a major chunk of itch's creator and userbase is trans, so there are a lot of cases where nudity in a product can't be strictly classed as one thing or another.)