My friend (who's already done with the archives whatever that is) tells me it's something to do with action scenes that bear a ton of reflection afterward? Like pages of text spent on analyzing why this or that was countered or the effects of this or that attack all in the space of one ingame second. Or something.
I dunno how to type out and interpret what she said over the phone
Overall she says it's got the same atmosphere as nasu's previous works, and she "likes Soujurou's and Aoko's interactions, kind of a new spin on a Shirou/Rin dynamic". And that it is an easy read, save for some particular kanji. And the system is "gorgeous, almost a new type of visual novel unto itself with unique presentation".