I don't think Gigguk has ever done a full - fledged review of the Fate visual novel. There are so many anime - related things to cover, and while the Fate series is popular, he might not have had the time or inclination to specifically review the visual novel. It's also possible that he feels that the anime adaptations are more accessible to his audience and thus focuses more on those rather than the original visual novel. However, this is all speculation as there's no concrete evidence either way.
I'm not sure specifically what Gigguk's opinion on the Fate visual novel is. He might like it for its complex storylines and diverse characters. Maybe he appreciates how it weaves together different mythologies.