It took me time to get to this post from my backlog, but I agree on most elements, really.

The filter played a weird role, the drawings themselves are good so the filter is unnecessary and doesn't really bring much of value, why do it?

I supposed they had good background and an historical setting but now that I read your info about how little information is known and that the author had some degree of freedom then I have to lower my score for it because it was severely lacking in the creativity department.

Honestly, it's decent, and like you said, thank god it's not ANOTHER sengoku one but it could have been done MUCH better. I also didn't like the attitude of the princess, she seems WAY too much forced or out of character, she was made just for the purpose of giving an heroine for the protagonist but lacks personality despite being a core figure.

Well, I guess I would recommend it too, but not for everyone :D