This is basically what Fate/staynight could have been. The format is kind of similar to a trailer.
First of all, the animation is absolutely fantastic, and the soundtrack isn't bad either.
In this version of the Holy Grail War, the main character is instead a girl called Ayaka, whose family was involved in the previous war. She doesn't want to get involved in the present war (apparently they take place every 8 years now). However, she gets attacked by Lancer, and ends up summoning Saber. Who is male.
The rest of the OVA is composed of really quick flashes of scenes and battles. It's confusing to watch, and
I had to go search online for more info about the characters and such in order to fully understand the OVA. There are many battle scenes in the OVA, and they all seem to be really epic. Special mention goes to Gilgamesh's new powers.
The characters are similar to Fate/staynight, given that this was the prototype for Staynight. The Servants have been slightly redesigned, including making Saber male. The protagonist Ayaka seems to be the generic scared & shy girl type, but then again the OVA didn't really give much time to develop anything. During the quick flashes, we get a glimpse at the villlains, all of which seem to be very interesting.
The character who stood out to me blonde girl at the very end who seems to be yandere for male!Saber. Later online searches tell me she is named Manaka, and she's actually Ayaka's sister and a main villan. She feels kind of like Illya to me.
Overall, I think this was a really cool concept. I really wish the OVA was longer, as a few searches online gave me some really interesting information that I didn't catch during the quick flashes.