I am a loyal fgo player so this may be a bit biased, the movie from the perspective of someone that haven't played fgo is quite good, but since i watched it and it's a movie, it seems very rushed if compared to the original material, I would expect the pace to be slower since it is 2 parts but this is quite the contrary, the character's don't have much time to be fully developed and some characters are cut completely from the story like Touta, and Hassan of Hundred Personas. The animation is still very good butunfortunately due to the high standards set by the Babylon anime and the Ufotable made ones, this is in my opinion, disappointing for a fate show. An example would be Tristan's fight, I have been very looking forward to it since in the game he attacks by strumming actual notes short melodies on the harp bow and arrows flies in from all directions. The casting of noble phantasms besides Stela also lacks the build up that is normally present in other shows. Small details like when Ozymandias' head slightly falls off due to reasons that would be spoilers (will be revealed in the second part hopefully) is also not included.
I have no huge complaints about the sound, it uses the source materials sound track and ost so it is nice. The song by Maaya Sakamoto is also awesome love it.
Like i have said in the beginning due to it being rushed character development is slightly overlooked, and some are completely removed, for new viewers that aren't loyal fans, they might be confused about the characters way of thinking and actions.
Overall i enjoyed it very much simply due to the fact that they adapted a story arc from fgo, the adaptation is still very good in general and would highly recommend for people that are already familirar with the fate franchise but for new viewers this may not be your thing.