1) Make the tags freeform
Tags are already freeform! We have a list of suggested tags that we encourage people to use though, it's easier to find certain things when people agree on tagging conventions. This topic is about finding the right tags to suggest to people creating tabletop games and the like.
2) Sidestep the media-bound classification
Tags can be anything, but at the moment it's impossible to browse all content by a tag, you have to select a primary content type (game, book, etc.). I'll think about this for a future update.