Since the question seems to asking for tags worth avoiding in the future, as well as tags that are already problematic, I'll add a speculative answer here.
In addition to the overly vague tags senshin listed, we could potentially end up with the opposite problem of overly specific tags. SciFi.SE has had some meta discussions about "character tags" which I think apply here too. It was summarized in this answer as follows:
the consensus based on recent meta discussions is that character tags should stick around if they identify some significant subset of question that a person might be an "expert" in. In other words, it's feasible that someone could know a whole lot about Darth Vader, but not really be interested in the rest of Star Wars. OTOH, it's less likely that someone would only want to answer questions about R2-D2 -- those questions will probably be answered by people who are general Star Wars experts.
So, for example, it might be okay for us to have tags like zeus or hercules since they have multiple stories that revolve primarily around them, and it's at least conceivable that someone would be knowledgeable about those specific stories, whereas "less popular characters" like themis or charon definitely wouldn't cut it.
Similarly, we should avoid making tags for individual books/scrolls/carvings/tablets, since as Jeff himself said, one tag for every novel ever written would be ridiculous.
