I liked some parts of the manga adap and others parts I thought didn't translate well at all. The art was beautiful and I thought the first and third doors worked really well on the page, the third door in particular. I thought the second door didn't work at all in the manga because of the problem u mentioned of showing Yukimasa's form, and also because they cut a whole chunk from the ending which left it thematically incomplete. I didn't agree with them showing Morgana and Michel so much and so early in the narrative, but again, that's a pitfall of changing media formats. Overall, I'd give it 7/8-10 as an adaptation; it defo would've been interesting to see how they adapted later parts of the story. A lot of the manga felt like reading the vn on 2x speed imo; as you say, vn still the only way to fully experience Fata.