The harem tag is probably used because the king's harem is a central part of the story. It doesn't really fit the standard use on this site (the MC having a harem) but I can still see how it applies. There is no romance tag, which signals to us that - at least so far - the main character is not in a relationship with any of the women.
I'm a fan of the harem, romance, and romcom genres so I can see why people might be frustrated. However, the story lays things out early on: the MC is a eunuch and therefore has "physical" limitations. If you're able to get past that, I think the story is very entertaining. That's why it's a little sad to see it getting review bombed on MAL. Just because it does not fit the mold people want it to fill doesn't mean it's a bad story.