I think that the low score of this anime lies to the fact that it refers to a small amount of people.
Not many understand the value of a peaceful, chilling anime. On the contrary, they seek action, romance, violence etc.
It may be based on history, but you don't really need to know anything,it's very easy to follow.
There is gentle comedy going on, pretty often, and it makes you laugh because of the naive, sweet humor.
The art is simple but beautiful, there is no intense drama or tension, and the script is minimalistic and relaxing.
I am impressed by the huge number of characters, and it's worth to be mentioned, they are male-ALL OF EM.
Everyone has their own unique personality, and it's expressed by their clothes, hairstyle, makeup etc. I really liked that.
Another thing I found extremely cute and touching, is the faith these sword-characters have in their master, and the strong bonds of friendship they share.
Of course, there is no way someone remembering all of the characters, I think there are proximately 50 of em-YEAH :')
You should watch it if you're lookin for sth peaceful, calm and relaxing.