I am a rinfag, however, that has nothing to with why I disliked Heaven's Feel 3 - especially considering Heaven's Feel is my favorite route.
Ufotable's HF adaptations fail to reach the emotional highs of the VN; For instance, Shirou's promise to Sakura in the rain is tarnished and nowhere near as emotionally satisfying, since the director choose to make the scene more about Sakura's complex rather than about Shirou's futile promise (Shirou knows he cannot protect her but he lies to herself and himself that he will - knowing it means his own death) and his pathological love for her. Instead, the Director makes the scene about Sakura's virginity and whether Shirou will accept her for this or not? Who cares? That was never what the scene was about
Another instance would be Nine Live's Blade works - the director fails to convey how grave the situation is; he fails to convey Shirou's burdens; he fails to convey how Shirou mentally surpasses Emiya to become his own man on a different path; he fails to convey how Shirou faces off against Hercules almost like a machine with utter perfection. The scene is stilted and misses all of the emotional impact.
Key characters like Illya and Kotomine are missing far too many scenes, which leads to a far weaker climax - Illya's sacrifice is nowhere near as touching because their sibling bond was never explored; and Kotomine's bond with Shirou feels contrived since Shirou doesn't have enough screen prescience woth him for their bond to feel believable.
And yet the director has the audacity to add filler such as Sakura's dream sequence in the second movie, he has the audacity to this while at the same time cutting out key scenes from the VN. It shows a clear lack of respect for the source material
I could go on and on, but these are some of my grievances with the HF trilogy