A 6. It isn't bad, but it has some things that keep it about average. It's TOS and characters and a universe I really like. I also like the lighting and moody atmosphere.
The women's transformation, particularly Eve, is something that can't be taken too literally even though that is the tendency for viewers when watching film or television. Beyond perhaps affecting a person's complexion and a few other things the Venus drug could well be causing the taker to put out powerful pheromones that affects the perception of others. That's the only explanation that really works for me. Later we will see Enterprise
women who are easily as beautiful or more so than Mudd's three so for the Enterprise
men to be so taken with Mudd's women (when under the drug's influence) suggests there's something else going on. In real life when we become infatuated or focused on someone we tend to see them to largely the exclusion of others, at least in the beginning. And we know there are definite biochemical changes happening to both men and women when we're "in love." So it could well be the Venus drug affects more than just the user.
In somewhat similar fashion is the Salt Vampire actually changing it's form or does it somehow affect the perceptions of others? How else to explain that different people can see different things at the same time? Kirk, McCoy and Darnell each saw "Nancy Crater" as someone different all at the same time. Later the creature learns to be more consistent in its appearance around Kirk and McCoy and others so it can influence what others are seeing so as not to cause confusion.
The idea of the dolled up women being "wiving settlers" isn't that far out as today there are any number of means for men of western countries to communicate with women from other countries interested in finding a mate abroad. And often these women (and men) can be made to seem more than what they actually are.
Harry Mudd establishes that TOS' future isn't perfect and ideal since there is obviously still crime only now taken to an interstellar scale. This episode also shows the role of Enterprise's
role as policeman as well as explorer and soldier.
It's a rather small scale story and Harry Mudd isn't particularly villianous or the situation all that dire. There are really no big stakes here.
Not horrible, not even bad, but just not exceptional either.