Well the tension of the fight suddenly ended abruptly, the weapon to do so hasn't come out of left field as we've known Kuro had an origin bullet on her for a while now. And with people wondering how they could even pull out a win in the first place, the origin bullet with what it did was a perfect answer.
Of course I'm unsure whether Darius is down for good. You never know with these things.
Also, Kuro's card got destroyed and she vanished. If that decision sticks, props to the author for that. Killing off a character is a very risky move in a series, and in this series it's always seemed to be a "we'll all win without loss" kind of story. Which can be fine but Fate has never been a series where the story always ended perfectly happily.