The best thing Ufotable did with this adaptation was mixing Ataraxia so well into the narrative. I was waiting for that german suplex to end the bout, but I guess Rin fans would not be happy seeing her actually lose (she did even in this episode, but it was only implied).
I love the height increase and slightly deeper voice for adult Shirou (not the weird olive green jacket, but meh). Not a fan of Rin's new hairdo, but that's a minor gripe. The dialog at the very end about Shirou's resolve was the best part for me. I love tragic heroes, even more so if they are rewarded at the end.
They even connected this story to another near the middle.
I think the Issei part was a waste of screen time, but the only other thing I would've wanted to see replace it was Saber popping back to life.
Masterpiece. I called it.
I imagine marathoning this would further cement that evaluation. It seems to be the type of story that greatly benefits from that.